diff --git a/mlir/examples/standalone/include/Standalone-c/Dialects.h b/mlir/examples/standalone/include/Standalone-c/Dialects.h
--- a/mlir/examples/standalone/include/Standalone-c/Dialects.h
+++ b/mlir/examples/standalone/include/Standalone-c/Dialects.h
@@ -9,7 +9,7 @@
 #ifndef STANDALONE_C_DIALECTS_H
 #define STANDALONE_C_DIALECTS_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/examples/standalone/python/CMakeLists.txt b/mlir/examples/standalone/python/CMakeLists.txt
--- a/mlir/examples/standalone/python/CMakeLists.txt
+++ b/mlir/examples/standalone/python/CMakeLists.txt
@@ -40,6 +40,9 @@
   RELATIVE_INSTALL_ROOT "../../../.."
   DECLARED_SOURCES
     StandalonePythonSources
+    # TODO: Remove this in favor of showing fine grained registration once
+    # available.
+    MLIRPythonExtension.RegisterEverything
     MLIRPythonSources.Core
 )
 
@@ -52,6 +55,9 @@
   INSTALL_PREFIX "python_packages/standalone/mlir_standalone"
   DECLARED_SOURCES
     StandalonePythonSources
+    # TODO: Remove this in favor of showing fine grained registration once
+    # available.
+    MLIRPythonExtension.RegisterEverything
     MLIRPythonSources
   COMMON_CAPI_LINK_LIBS
     StandalonePythonCAPI
diff --git a/mlir/examples/standalone/test/CAPI/CMakeLists.txt b/mlir/examples/standalone/test/CAPI/CMakeLists.txt
--- a/mlir/examples/standalone/test/CAPI/CMakeLists.txt
+++ b/mlir/examples/standalone/test/CAPI/CMakeLists.txt
@@ -6,7 +6,9 @@
   SHARED
   EMBED_LIBS
   MLIRCAPIIR
-  MLIRCAPIRegistration
+  # TODO: Remove this in favor of showing fine grained dialect registration
+  # (once available).
+  MLIRCAPIRegisterEverything
   StandaloneCAPI
 )
 
diff --git a/mlir/examples/standalone/test/CAPI/standalone-capi-test.c b/mlir/examples/standalone/test/CAPI/standalone-capi-test.c
--- a/mlir/examples/standalone/test/CAPI/standalone-capi-test.c
+++ b/mlir/examples/standalone/test/CAPI/standalone-capi-test.c
@@ -11,14 +11,22 @@
 
 #include <stdio.h>
 
-#include "mlir-c/IR.h"
 #include "Standalone-c/Dialects.h"
+#include "mlir-c/IR.h"
+#include "mlir-c/RegisterEverything.h"
+
+static void registerAllUpstreamDialects(MlirContext ctx) {
+  MlirDialectRegistry registry = mlirDialectRegistryCreate();
+  mlirRegisterAllDialects(registry);
+  mlirContextAppendDialectRegistry(ctx, registry);
+  mlirDialectRegistryDestroy(registry);
+}
 
 int main(int argc, char **argv) {
   MlirContext ctx = mlirContextCreate();
   // TODO: Create the dialect handles for the builtin dialects and avoid this.
   // This adds dozens of MB of binary size over just the standalone dialect.
-  mlirRegisterAllDialects(ctx);
+  registerAllUpstreamDialects(ctx);
   mlirDialectHandleRegisterDialect(mlirGetDialectHandle__standalone__(), ctx);
 
   MlirModule module = mlirModuleCreateParse(
diff --git a/mlir/include/mlir-c/Bindings/Python/Interop.h b/mlir/include/mlir-c/Bindings/Python/Interop.h
--- a/mlir/include/mlir-c/Bindings/Python/Interop.h
+++ b/mlir/include/mlir-c/Bindings/Python/Interop.h
@@ -64,6 +64,8 @@
   MAKE_MLIR_PYTHON_QUALNAME("ir.Attribute._CAPIPtr")
 #define MLIR_PYTHON_CAPSULE_CONTEXT                                            \
   MAKE_MLIR_PYTHON_QUALNAME("ir.Context._CAPIPtr")
+#define MLIR_PYTHON_CAPSULE_DIALECT_REGISTRY                                   \
+  MAKE_MLIR_PYTHON_QUALNAME("ir.DialectRegistry._CAPIPtr")
 #define MLIR_PYTHON_CAPSULE_EXECUTION_ENGINE                                   \
   MAKE_MLIR_PYTHON_QUALNAME("execution_engine.ExecutionEngine._CAPIPtr")
 #define MLIR_PYTHON_CAPSULE_INTEGER_SET                                        \
@@ -172,6 +174,28 @@
   return context;
 }
 
+/** Creates a capsule object encapsulating the raw C-API MlirDialectRegistry.
+ * The returned capsule does not extend or affect ownership of any Python
+ * objects that reference the context in any way.
+ */
+static inline PyObject *
+mlirPythonDialectRegistryToCapsule(MlirDialectRegistry registry) {
+  return PyCapsule_New(registry.ptr, MLIR_PYTHON_CAPSULE_DIALECT_REGISTRY,
+                       NULL);
+}
+
+/** Extracts an MlirDialectRegistry from a capsule as produced from
+ * mlirPythonDialectRegistryToCapsule. If the capsule is not of the right type,
+ * then a null context is returned (as checked via mlirContextIsNull). In such a
+ * case, the Python APIs will have already set an error. */
+static inline MlirDialectRegistry
+mlirPythonCapsuleToDialectRegistry(PyObject *capsule) {
+  void *ptr =
+      PyCapsule_GetPointer(capsule, MLIR_PYTHON_CAPSULE_DIALECT_REGISTRY);
+  MlirDialectRegistry registry = {ptr};
+  return registry;
+}
+
 /** Creates a capsule object encapsulating the raw C-API MlirLocation.
  * The returned capsule does not extend or affect ownership of any Python
  * objects that reference the location in any way. */
diff --git a/mlir/include/mlir-c/Dialect/Async.h b/mlir/include/mlir-c/Dialect/Async.h
--- a/mlir/include/mlir-c/Dialect/Async.h
+++ b/mlir/include/mlir-c/Dialect/Async.h
@@ -10,7 +10,7 @@
 #ifndef MLIR_C_DIALECT_ASYNC_H
 #define MLIR_C_DIALECT_ASYNC_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 #include "mlir-c/Support.h"
 
 #ifdef __cplusplus
diff --git a/mlir/include/mlir-c/Dialect/ControlFlow.h b/mlir/include/mlir-c/Dialect/ControlFlow.h
--- a/mlir/include/mlir-c/Dialect/ControlFlow.h
+++ b/mlir/include/mlir-c/Dialect/ControlFlow.h
@@ -10,7 +10,7 @@
 #ifndef MLIR_C_DIALECT_CONTROLFLOW_H
 #define MLIR_C_DIALECT_CONTROLFLOW_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/Dialect/Func.h b/mlir/include/mlir-c/Dialect/Func.h
--- a/mlir/include/mlir-c/Dialect/Func.h
+++ b/mlir/include/mlir-c/Dialect/Func.h
@@ -18,7 +18,7 @@
 #ifndef MLIR_C_DIALECT_FUNC_H
 #define MLIR_C_DIALECT_FUNC_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/Dialect/GPU.h b/mlir/include/mlir-c/Dialect/GPU.h
--- a/mlir/include/mlir-c/Dialect/GPU.h
+++ b/mlir/include/mlir-c/Dialect/GPU.h
@@ -10,7 +10,7 @@
 #ifndef MLIR_C_DIALECT_GPU_H
 #define MLIR_C_DIALECT_GPU_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 #include "mlir-c/Support.h"
 
 #ifdef __cplusplus
diff --git a/mlir/include/mlir-c/Dialect/LLVM.h b/mlir/include/mlir-c/Dialect/LLVM.h
--- a/mlir/include/mlir-c/Dialect/LLVM.h
+++ b/mlir/include/mlir-c/Dialect/LLVM.h
@@ -11,7 +11,6 @@
 #define MLIR_C_DIALECT_LLVM_H
 
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/Dialect/Linalg.h b/mlir/include/mlir-c/Dialect/Linalg.h
--- a/mlir/include/mlir-c/Dialect/Linalg.h
+++ b/mlir/include/mlir-c/Dialect/Linalg.h
@@ -10,7 +10,7 @@
 #ifndef MLIR_C_DIALECT_LINALG_H
 #define MLIR_C_DIALECT_LINALG_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 #include "mlir-c/Support.h"
 
 #ifdef __cplusplus
diff --git a/mlir/include/mlir-c/Dialect/PDL.h b/mlir/include/mlir-c/Dialect/PDL.h
--- a/mlir/include/mlir-c/Dialect/PDL.h
+++ b/mlir/include/mlir-c/Dialect/PDL.h
@@ -11,7 +11,6 @@
 #define MLIR_C_DIALECT_PDL_H
 
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/Dialect/Quant.h b/mlir/include/mlir-c/Dialect/Quant.h
--- a/mlir/include/mlir-c/Dialect/Quant.h
+++ b/mlir/include/mlir-c/Dialect/Quant.h
@@ -11,7 +11,6 @@
 #define MLIR_C_DIALECT_QUANT_H
 
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/Dialect/SCF.h b/mlir/include/mlir-c/Dialect/SCF.h
--- a/mlir/include/mlir-c/Dialect/SCF.h
+++ b/mlir/include/mlir-c/Dialect/SCF.h
@@ -10,7 +10,7 @@
 #ifndef MLIR_C_DIALECT_SCF_H
 #define MLIR_C_DIALECT_SCF_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/Dialect/Shape.h b/mlir/include/mlir-c/Dialect/Shape.h
--- a/mlir/include/mlir-c/Dialect/Shape.h
+++ b/mlir/include/mlir-c/Dialect/Shape.h
@@ -10,7 +10,7 @@
 #ifndef MLIR_C_DIALECT_SHAPE_H
 #define MLIR_C_DIALECT_SHAPE_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/Dialect/SparseTensor.h b/mlir/include/mlir-c/Dialect/SparseTensor.h
--- a/mlir/include/mlir-c/Dialect/SparseTensor.h
+++ b/mlir/include/mlir-c/Dialect/SparseTensor.h
@@ -11,7 +11,7 @@
 #define MLIR_C_DIALECT_SPARSETENSOR_H
 
 #include "mlir-c/AffineMap.h"
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/Dialect/Tensor.h b/mlir/include/mlir-c/Dialect/Tensor.h
--- a/mlir/include/mlir-c/Dialect/Tensor.h
+++ b/mlir/include/mlir-c/Dialect/Tensor.h
@@ -10,7 +10,7 @@
 #ifndef MLIR_C_DIALECT_TENSOR_H
 #define MLIR_C_DIALECT_TENSOR_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/include/mlir-c/IR.h b/mlir/include/mlir-c/IR.h
--- a/mlir/include/mlir-c/IR.h
+++ b/mlir/include/mlir-c/IR.h
@@ -130,6 +130,11 @@
 MLIR_CAPI_EXPORTED void mlirContextEnableMultithreading(MlirContext context,
                                                         bool enable);
 
+/// Eagerly loads all available dialects registered with a context, making
+/// them available for use for IR construction.
+MLIR_CAPI_EXPORTED void
+mlirContextLoadAllAvailableDialects(MlirContext context);
+
 /// Returns whether the given fully-qualified operation (i.e.
 /// 'dialect.operation') is registered with the context. This will return true
 /// if the dialect is loaded and the operation is registered within the
@@ -157,6 +162,47 @@
 /// Returns the namespace of the given dialect.
 MLIR_CAPI_EXPORTED MlirStringRef mlirDialectGetNamespace(MlirDialect dialect);
 
+//===----------------------------------------------------------------------===//
+// DialectHandle API.
+// Registration entry-points for each dialect are declared using the common
+// MLIR_DECLARE_DIALECT_REGISTRATION_CAPI macro, which takes the dialect
+// API name (i.e. "Func", "Tensor", "Linalg") and namespace (i.e. "func",
+// "tensor", "linalg"). The following declarations are produced:
+//
+//   /// Gets the above hook methods in struct form for a dialect by namespace.
+//   /// This is intended to facilitate dynamic lookup and registration of
+//   /// dialects via a plugin facility based on shared library symbol lookup.
+//   const MlirDialectHandle *mlirGetDialectHandle__{NAMESPACE}__();
+//
+// This is done via a common macro to facilitate future expansion to
+// registration schemes.
+//===----------------------------------------------------------------------===//
+
+struct MlirDialectHandle {
+  const void *ptr;
+};
+typedef struct MlirDialectHandle MlirDialectHandle;
+
+#define MLIR_DECLARE_CAPI_DIALECT_REGISTRATION(Name, Namespace)                \
+  MLIR_CAPI_EXPORTED MlirDialectHandle mlirGetDialectHandle__##Namespace##__()
+
+/// Returns the namespace associated with the provided dialect handle.
+MLIR_CAPI_EXPORTED
+MlirStringRef mlirDialectHandleGetNamespace(MlirDialectHandle);
+
+/// Inserts the dialect associated with the provided dialect handle into the
+/// provided dialect registry
+MLIR_CAPI_EXPORTED void mlirDialectHandleInsertDialect(MlirDialectHandle,
+                                                       MlirDialectRegistry);
+
+/// Registers the dialect associated with the provided dialect handle.
+MLIR_CAPI_EXPORTED void mlirDialectHandleRegisterDialect(MlirDialectHandle,
+                                                         MlirContext);
+
+/// Loads the dialect associated with the provided dialect handle.
+MLIR_CAPI_EXPORTED MlirDialect mlirDialectHandleLoadDialect(MlirDialectHandle,
+                                                            MlirContext);
+
 //===----------------------------------------------------------------------===//
 // DialectRegistry API.
 //===----------------------------------------------------------------------===//
diff --git a/mlir/include/mlir-c/Pass.h b/mlir/include/mlir-c/Pass.h
--- a/mlir/include/mlir-c/Pass.h
+++ b/mlir/include/mlir-c/Pass.h
@@ -15,7 +15,6 @@
 #define MLIR_C_PASS_H
 
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
 #include "mlir-c/Support.h"
 
 #ifdef __cplusplus
diff --git a/mlir/include/mlir-c/RegisterEverything.h b/mlir/include/mlir-c/RegisterEverything.h
new file mode 100644
--- /dev/null
+++ b/mlir/include/mlir-c/RegisterEverything.h
@@ -0,0 +1,38 @@
+//===-- mlir-c/RegisterEverything.h - Register all MLIR entities --*- C -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM
+// Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// This header contains registration entry points for MLIR upstream dialects
+// and passes. Downstream projects typically will not want to use this unless
+// if they don't care about binary size or build bloat and just wish access
+// to the entire set of upstream facilities. For those that do care, they
+// should use registration functions specific to their project.
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_C_REGISTER_EVERYTHING_H
+#define MLIR_C_REGISTER_EVERYTHING_H
+
+#include "mlir-c/IR.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/// Appends all upstream dialects and extensions to the dialect registry.
+MLIR_CAPI_EXPORTED void mlirRegisterAllDialects(MlirDialectRegistry registry);
+
+/// Register all translations to LLVM IR for dialects that can support it.
+MLIR_CAPI_EXPORTED void mlirRegisterAllLLVMTranslations(MlirContext context);
+
+/// Register all compiler passes of MLIR.
+MLIR_CAPI_EXPORTED void mlirRegisterAllPasses();
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // MLIR_C_REGISTER_EVERYTHING_H
diff --git a/mlir/include/mlir-c/Registration.h b/mlir/include/mlir-c/Registration.h
deleted file mode 100644
--- a/mlir/include/mlir-c/Registration.h
+++ /dev/null
@@ -1,75 +0,0 @@
-//===-- mlir-c/Registration.h - Registration functions for MLIR ---*- C -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM
-// Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef MLIR_C_REGISTRATION_H
-#define MLIR_C_REGISTRATION_H
-
-#include "mlir-c/IR.h"
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-//===----------------------------------------------------------------------===//
-// Dialect registration declarations.
-// Registration entry-points for each dialect are declared using the common
-// MLIR_DECLARE_DIALECT_REGISTRATION_CAPI macro, which takes the dialect
-// API name (i.e. "Func", "Tensor", "Linalg") and namespace (i.e. "func",
-// "tensor", "linalg"). The following declarations are produced:
-//
-//   /// Gets the above hook methods in struct form for a dialect by namespace.
-//   /// This is intended to facilitate dynamic lookup and registration of
-//   /// dialects via a plugin facility based on shared library symbol lookup.
-//   const MlirDialectHandle *mlirGetDialectHandle__{NAMESPACE}__();
-//
-// This is done via a common macro to facilitate future expansion to
-// registration schemes.
-//===----------------------------------------------------------------------===//
-
-struct MlirDialectHandle {
-  const void *ptr;
-};
-typedef struct MlirDialectHandle MlirDialectHandle;
-
-#define MLIR_DECLARE_CAPI_DIALECT_REGISTRATION(Name, Namespace)                \
-  MLIR_CAPI_EXPORTED MlirDialectHandle mlirGetDialectHandle__##Namespace##__()
-
-/// Returns the namespace associated with the provided dialect handle.
-MLIR_CAPI_EXPORTED
-MlirStringRef mlirDialectHandleGetNamespace(MlirDialectHandle);
-
-/// Inserts the dialect associated with the provided dialect handle into the
-/// provided dialect registry
-MLIR_CAPI_EXPORTED void mlirDialectHandleInsertDialect(MlirDialectHandle,
-                                                       MlirDialectRegistry);
-
-/// Registers the dialect associated with the provided dialect handle.
-MLIR_CAPI_EXPORTED void mlirDialectHandleRegisterDialect(MlirDialectHandle,
-                                                         MlirContext);
-
-/// Loads the dialect associated with the provided dialect handle.
-MLIR_CAPI_EXPORTED MlirDialect mlirDialectHandleLoadDialect(MlirDialectHandle,
-                                                            MlirContext);
-
-/// Registers all dialects known to core MLIR with the provided Context.
-/// This is needed before creating IR for these Dialects.
-/// TODO: Remove this function once the real registration API is finished.
-MLIR_CAPI_EXPORTED void mlirRegisterAllDialects(MlirContext context);
-
-/// Register all translations to LLVM IR for dialects that can support it.
-MLIR_CAPI_EXPORTED void mlirRegisterAllLLVMTranslations(MlirContext context);
-
-/// Register all compiler passes of MLIR.
-MLIR_CAPI_EXPORTED void mlirRegisterAllPasses();
-
-#ifdef __cplusplus
-}
-#endif
-
-#endif // MLIR_C_REGISTRATION_H
diff --git a/mlir/include/mlir/Bindings/Python/PybindAdaptors.h b/mlir/include/mlir/Bindings/Python/PybindAdaptors.h
--- a/mlir/include/mlir/Bindings/Python/PybindAdaptors.h
+++ b/mlir/include/mlir/Bindings/Python/PybindAdaptors.h
@@ -124,6 +124,25 @@
   }
 };
 
+/// Casts object <-> MlirDialectRegistry.
+template <>
+struct type_caster<MlirDialectRegistry> {
+  PYBIND11_TYPE_CASTER(MlirDialectRegistry, _("MlirDialectRegistry"));
+  bool load(handle src, bool) {
+    py::object capsule = mlirApiObjectToCapsule(src);
+    value = mlirPythonCapsuleToDialectRegistry(capsule.ptr());
+    return !mlirDialectRegistryIsNull(value);
+  }
+  static handle cast(MlirDialectRegistry v, return_value_policy, handle) {
+    py::object capsule = py::reinterpret_steal<py::object>(
+        mlirPythonDialectRegistryToCapsule(v));
+    return py::module::import(MAKE_MLIR_PYTHON_QUALNAME("ir"))
+        .attr("DialectRegistry")
+        .attr(MLIR_PYTHON_CAPI_FACTORY_ATTR)(capsule)
+        .release();
+  }
+};
+
 /// Casts object <-> MlirLocation.
 template <>
 struct type_caster<MlirLocation> {
diff --git a/mlir/include/mlir/CAPI/Registration.h b/mlir/include/mlir/CAPI/Registration.h
--- a/mlir/include/mlir/CAPI/Registration.h
+++ b/mlir/include/mlir/CAPI/Registration.h
@@ -10,7 +10,6 @@
 #define MLIR_CAPI_REGISTRATION_H
 
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
 #include "mlir/CAPI/IR.h"
 #include "mlir/CAPI/Support.h"
 
diff --git a/mlir/lib/Bindings/Python/AllPassesRegistration.cpp b/mlir/lib/Bindings/Python/AllPassesRegistration.cpp
deleted file mode 100644
--- a/mlir/lib/Bindings/Python/AllPassesRegistration.cpp
+++ /dev/null
@@ -1,22 +0,0 @@
-//===- AllPassesRegistration.cpp - Pybind module to register all passes ---===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "mlir-c/Registration.h"
-
-#include <pybind11/pybind11.h>
-
-// -----------------------------------------------------------------------------
-// Module initialization.
-// -----------------------------------------------------------------------------
-
-PYBIND11_MODULE(_mlirAllPassesRegistration, m) {
-  m.doc() = "MLIR All Passes Convenience Module";
-
-  // Register all passes on load.
-  mlirRegisterAllPasses();
-}
diff --git a/mlir/lib/Bindings/Python/Conversions/Conversions.cpp b/mlir/lib/Bindings/Python/Conversions/Conversions.cpp
deleted file mode 100644
--- a/mlir/lib/Bindings/Python/Conversions/Conversions.cpp
+++ /dev/null
@@ -1,22 +0,0 @@
-//===- Conversions.cpp - Pybind module for the Conversionss library -------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "mlir-c/Conversion.h"
-
-#include <pybind11/pybind11.h>
-
-// -----------------------------------------------------------------------------
-// Module initialization.
-// -----------------------------------------------------------------------------
-
-PYBIND11_MODULE(_mlirConversions, m) {
-  m.doc() = "MLIR Conversions library";
-
-  // Register all the passes in the Conversions library on load.
-  mlirRegisterConversionPasses();
-}
diff --git a/mlir/lib/Bindings/Python/IRCore.cpp b/mlir/lib/Bindings/Python/IRCore.cpp
--- a/mlir/lib/Bindings/Python/IRCore.cpp
+++ b/mlir/lib/Bindings/Python/IRCore.cpp
@@ -16,7 +16,7 @@
 #include "mlir-c/BuiltinTypes.h"
 #include "mlir-c/Debug.h"
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
+//#include "mlir-c/Registration.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
 
@@ -474,7 +474,6 @@
 
 PyMlirContext *PyMlirContext::createNewContextForInit() {
   MlirContext context = mlirContextCreate();
-  mlirRegisterAllDialects(context);
   return new PyMlirContext(context);
 }
 
@@ -793,7 +792,7 @@
 }
 
 //------------------------------------------------------------------------------
-// PyDialect, PyDialectDescriptor, PyDialects
+// PyDialect, PyDialectDescriptor, PyDialects, PyDialectRegistry
 //------------------------------------------------------------------------------
 
 MlirDialect PyDialects::getDialectForKey(const std::string &key,
@@ -807,6 +806,19 @@
   return dialect;
 }
 
+py::object PyDialectRegistry::getCapsule() {
+  return py::reinterpret_steal<py::object>(
+      mlirPythonDialectRegistryToCapsule(*this));
+}
+
+PyDialectRegistry PyDialectRegistry::createFromCapsule(py::object capsule) {
+  MlirDialectRegistry rawRegistry =
+      mlirPythonCapsuleToDialectRegistry(capsule.ptr());
+  if (mlirDialectRegistryIsNull(rawRegistry))
+    throw py::error_already_set();
+  return PyDialectRegistry(rawRegistry);
+}
+
 //------------------------------------------------------------------------------
 // PyLocation
 //------------------------------------------------------------------------------
@@ -2207,8 +2219,11 @@
 
   //----------------------------------------------------------------------------
   // Mapping of MlirContext.
+  // Note that this is exported as _BaseContext. The containing, Python level
+  // __init__.py will subclass it with site-specific functionality and set a
+  // "Context" attribute on this module.
   //----------------------------------------------------------------------------
-  py::class_<PyMlirContext>(m, "Context", py::module_local())
+  py::class_<PyMlirContext>(m, "_BaseContext", py::module_local())
       .def(py::init<>(&PyMlirContext::createNewContextForInit))
       .def_static("_get_live_count", &PyMlirContext::getLiveCount)
       .def("_get_context_again",
@@ -2276,7 +2291,16 @@
             return mlirContextIsRegisteredOperation(
                 self.get(), MlirStringRef{name.data(), name.size()});
           },
-          py::arg("operation_name"));
+          py::arg("operation_name"))
+      .def(
+          "append_dialect_registry",
+          [](PyMlirContext &self, PyDialectRegistry &registry) {
+            mlirContextAppendDialectRegistry(self.get(), registry);
+          },
+          py::arg("registry"))
+      .def("load_all_available_dialects", [](PyMlirContext &self) {
+        mlirContextLoadAllAvailableDialects(self.get());
+      });
 
   //----------------------------------------------------------------------------
   // Mapping of PyDialectDescriptor
@@ -2331,6 +2355,15 @@
                clazz.attr("__name__") + py::str(")>");
       });
 
+  //----------------------------------------------------------------------------
+  // Mapping of PyDialectRegistry
+  //----------------------------------------------------------------------------
+  py::class_<PyDialectRegistry>(m, "DialectRegistry", py::module_local())
+      .def_property_readonly(MLIR_PYTHON_CAPI_PTR_ATTR,
+                             &PyDialectRegistry::getCapsule)
+      .def(MLIR_PYTHON_CAPI_FACTORY_ATTR, &PyDialectRegistry::createFromCapsule)
+      .def(py::init<>());
+
   //----------------------------------------------------------------------------
   // Mapping of Location
   //----------------------------------------------------------------------------
diff --git a/mlir/lib/Bindings/Python/IRModule.h b/mlir/lib/Bindings/Python/IRModule.h
--- a/mlir/lib/Bindings/Python/IRModule.h
+++ b/mlir/lib/Bindings/Python/IRModule.h
@@ -390,6 +390,32 @@
   pybind11::object descriptor;
 };
 
+/// Wrapper around an MlirDialectRegistry.
+/// Upon construction, the Python wrapper takes ownership of the
+/// underlying MlirDialectRegistry.
+class PyDialectRegistry {
+public:
+  PyDialectRegistry() : registry(mlirDialectRegistryCreate()) {}
+  PyDialectRegistry(MlirDialectRegistry registry) : registry(registry) {}
+  ~PyDialectRegistry() {
+    if (!mlirDialectRegistryIsNull(registry))
+      mlirDialectRegistryDestroy(registry);
+  }
+  PyDialectRegistry(PyDialectRegistry &) = delete;
+  PyDialectRegistry(PyDialectRegistry &&other) : registry(other.registry) {
+    other.registry = {nullptr};
+  }
+
+  operator MlirDialectRegistry() const { return registry; }
+  MlirDialectRegistry get() const { return registry; }
+
+  pybind11::object getCapsule();
+  static PyDialectRegistry createFromCapsule(pybind11::object capsule);
+
+private:
+  MlirDialectRegistry registry;
+};
+
 /// Wrapper around an MlirLocation.
 class PyLocation : public BaseContextObject {
 public:
diff --git a/mlir/lib/Bindings/Python/RegisterEverything.cpp b/mlir/lib/Bindings/Python/RegisterEverything.cpp
new file mode 100644
--- /dev/null
+++ b/mlir/lib/Bindings/Python/RegisterEverything.cpp
@@ -0,0 +1,26 @@
+//===- RegisterEverything.cpp - API to register all dialects/passes -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir-c/RegisterEverything.h"
+#include "mlir-c/Conversion.h"
+#include "mlir-c/Transforms.h"
+
+#include "mlir/Bindings/Python/PybindAdaptors.h"
+
+PYBIND11_MODULE(_mlirRegisterEverything, m) {
+  m.doc() = "MLIR All Upstream Dialects and Passes Registration";
+
+  m.def("register_dialects", [](MlirDialectRegistry registry) {
+    mlirRegisterAllDialects(registry);
+  });
+
+  // Register all passes on load.
+  mlirRegisterAllPasses();
+  mlirRegisterConversionPasses();
+  mlirRegisterTransformsPasses();
+}
diff --git a/mlir/lib/Bindings/Python/Transforms/Transforms.cpp b/mlir/lib/Bindings/Python/Transforms/Transforms.cpp
deleted file mode 100644
--- a/mlir/lib/Bindings/Python/Transforms/Transforms.cpp
+++ /dev/null
@@ -1,22 +0,0 @@
-//===- Transforms.cpp - Pybind module for the Transforms library ----------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "mlir-c/Transforms.h"
-
-#include <pybind11/pybind11.h>
-
-// -----------------------------------------------------------------------------
-// Module initialization.
-// -----------------------------------------------------------------------------
-
-PYBIND11_MODULE(_mlirTransforms, m) {
-  m.doc() = "MLIR Transforms library";
-
-  // Register all the passes in the Transforms library on load.
-  mlirRegisterTransformsPasses();
-}
diff --git a/mlir/lib/CAPI/CMakeLists.txt b/mlir/lib/CAPI/CMakeLists.txt
--- a/mlir/lib/CAPI/CMakeLists.txt
+++ b/mlir/lib/CAPI/CMakeLists.txt
@@ -12,7 +12,7 @@
 add_subdirectory(Conversion)
 add_subdirectory(Interfaces)
 add_subdirectory(IR)
-add_subdirectory(Registration)
+add_subdirectory(RegisterEverything)
 add_subdirectory(Transforms)
 
 # Only enable the ExecutionEngine if the native target is configured in.
diff --git a/mlir/lib/CAPI/Conversion/CMakeLists.txt b/mlir/lib/CAPI/Conversion/CMakeLists.txt
--- a/mlir/lib/CAPI/Conversion/CMakeLists.txt
+++ b/mlir/lib/CAPI/Conversion/CMakeLists.txt
@@ -2,6 +2,9 @@
 add_mlir_upstream_c_api_library(MLIRCAPIConversion
   Passes.cpp
 
+  DEPENDS
+  MLIRConversionPassIncGen
+
   LINK_LIBS PUBLIC
   ${conversion_libs}
 )
diff --git a/mlir/lib/CAPI/IR/IR.cpp b/mlir/lib/CAPI/IR/IR.cpp
--- a/mlir/lib/CAPI/IR/IR.cpp
+++ b/mlir/lib/CAPI/IR/IR.cpp
@@ -77,6 +77,10 @@
   return unwrap(context)->enableMultithreading(enable);
 }
 
+void mlirContextLoadAllAvailableDialects(MlirContext context) {
+  unwrap(context)->loadAllAvailableDialects();
+}
+
 //===----------------------------------------------------------------------===//
 // Dialect API.
 //===----------------------------------------------------------------------===//
diff --git a/mlir/lib/CAPI/Registration/CMakeLists.txt b/mlir/lib/CAPI/RegisterEverything/CMakeLists.txt
rename from mlir/lib/CAPI/Registration/CMakeLists.txt
rename to mlir/lib/CAPI/RegisterEverything/CMakeLists.txt
--- a/mlir/lib/CAPI/Registration/CMakeLists.txt
+++ b/mlir/lib/CAPI/RegisterEverything/CMakeLists.txt
@@ -2,13 +2,15 @@
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 get_property(translation_libs GLOBAL PROPERTY MLIR_TRANSLATION_LIBS)
 get_property(conversion_libs GLOBAL PROPERTY MLIR_CONVERSION_LIBS)
-add_mlir_upstream_c_api_library(MLIRCAPIRegistration
-  Registration.cpp
+add_mlir_upstream_c_api_library(MLIRCAPIRegisterEverything
+  RegisterEverything.cpp
 
   LINK_LIBS PUBLIC
-  MLIRCAPIIR
-  MLIRLLVMToLLVMIRTranslation
   ${dialect_libs}
   ${translation_libs}
   ${conversion_libs}
+
+  MLIRCAPIIR
+  MLIRLLVMToLLVMIRTranslation
+  MLIRCAPITransforms
 )
diff --git a/mlir/lib/CAPI/Registration/Registration.cpp b/mlir/lib/CAPI/RegisterEverything/RegisterEverything.cpp
rename from mlir/lib/CAPI/Registration/Registration.cpp
rename to mlir/lib/CAPI/RegisterEverything/RegisterEverything.cpp
--- a/mlir/lib/CAPI/Registration/Registration.cpp
+++ b/mlir/lib/CAPI/RegisterEverything/RegisterEverything.cpp
@@ -1,4 +1,4 @@
-//===- Registration.cpp - C Interface for MLIR Registration ---------------===//
+//===- RegisterEverything.cpp - Register all MLIR entities ----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,17 +6,15 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/RegisterEverything.h"
 
 #include "mlir/CAPI/IR.h"
 #include "mlir/InitAllDialects.h"
 #include "mlir/InitAllPasses.h"
 #include "mlir/Target/LLVMIR/Dialect/LLVMIR/LLVMToLLVMIRTranslation.h"
 
-void mlirRegisterAllDialects(MlirContext context) {
-  mlir::registerAllDialects(*unwrap(context));
-  // TODO: we may not want to eagerly load here.
-  unwrap(context)->loadAllAvailableDialects();
+void mlirRegisterAllDialects(MlirDialectRegistry registry) {
+  mlir::registerAllDialects(*unwrap(registry));
 }
 
 void mlirRegisterAllLLVMTranslations(MlirContext context) {
diff --git a/mlir/python/CMakeLists.txt b/mlir/python/CMakeLists.txt
--- a/mlir/python/CMakeLists.txt
+++ b/mlir/python/CMakeLists.txt
@@ -37,17 +37,8 @@
     runtime/*.py
 )
 
-declare_mlir_python_sources(MLIRPythonSources.Passes
-  ROOT_DIR "${CMAKE_CURRENT_SOURCE_DIR}/mlir"
-  ADD_TO_PARENT MLIRPythonSources
-  SOURCES_GLOB
-    all_passes_registration/*.py
-    conversions/*.py
-    transforms/*.py
-)
-
 declare_mlir_python_sources(MLIRPythonCAPI.HeaderSources
-  ROOT_DIR "${MLIR_MAIN_INCLUDE_DIR}"
+  ROOT_DIR "${MLIR_SOURCE_DIR}/include"
   SOURCES_GLOB "mlir-c/*.h"
 )
 
@@ -283,12 +274,31 @@
     MLIRCAPIDebug
     MLIRCAPIIR
     MLIRCAPIInterfaces
-    MLIRCAPIRegistration  # TODO: See about dis-aggregating
 
     # Dialects
     MLIRCAPIFunc
 )
 
+# This extension exposes an API to register all dialects, extensions, and passes
+# packaged in upstream MLIR and it is used for the upstream "mlir" Python
+# package. Downstreams will likely want to provide their own and not depend
+# on this one, since it links in the world.
+# Note that this is not added to any top-level source target for transitive
+# inclusion: It must be included explicitly by downstreams if desired. Note that
+# this has a very large impact on what gets built/packaged.
+declare_mlir_python_extension(MLIRPythonExtension.RegisterEverything
+  MODULE_NAME _mlirRegisterEverything
+  ROOT_DIR "${PYTHON_SOURCE_DIR}"
+  SOURCES
+    RegisterEverything.cpp
+  PRIVATE_LINK_LIBS
+    LLVMSupport
+  EMBED_CAPI_LINK_LIBS
+    MLIRCAPIConversion
+    MLIRCAPITransforms
+    MLIRCAPIRegisterEverything
+)
+
 declare_mlir_python_extension(MLIRPythonExtension.Dialects.Linalg.Pybind
   MODULE_NAME _mlirDialectsLinalg
   ADD_TO_PARENT MLIRPythonSources.Dialects.linalg
@@ -341,18 +351,6 @@
     MLIRCAPISparseTensor
 )
 
-declare_mlir_python_extension(MLIRPythonExtension.AllPassesRegistration
-  MODULE_NAME _mlirAllPassesRegistration
-  ROOT_DIR "${PYTHON_SOURCE_DIR}"
-  SOURCES
-    AllPassesRegistration.cpp
-  PRIVATE_LINK_LIBS
-    LLVMSupport
-  EMBED_CAPI_LINK_LIBS
-    MLIRCAPIConversion
-    MLIRCAPITransforms
-)
-
 declare_mlir_python_extension(MLIRPythonExtension.AsyncDialectPasses
   MODULE_NAME _mlirAsyncPasses
   ADD_TO_PARENT MLIRPythonSources.Dialects.async_dialect
@@ -365,18 +363,6 @@
     MLIRCAPIAsync
 )
 
-declare_mlir_python_extension(MLIRPythonExtension.Conversions
-  MODULE_NAME _mlirConversions
-  ADD_TO_PARENT MLIRPythonSources.Passes
-  ROOT_DIR "${PYTHON_SOURCE_DIR}"
-  SOURCES
-    Conversions/Conversions.cpp
-  PRIVATE_LINK_LIBS
-    LLVMSupport
-  EMBED_CAPI_LINK_LIBS
-  MLIRCAPIConversion
-)
-
 # Only enable the ExecutionEngine if the native target is configured in.
 if(TARGET ${LLVM_NATIVE_ARCH})
   declare_mlir_python_extension(MLIRPythonExtension.ExecutionEngine
@@ -428,18 +414,6 @@
     MLIRCAPISparseTensor
 )
 
-declare_mlir_python_extension(MLIRPythonExtension.Transforms
-  MODULE_NAME _mlirTransforms
-  ADD_TO_PARENT MLIRPythonSources.Passes
-  ROOT_DIR "${PYTHON_SOURCE_DIR}"
-  SOURCES
-    Transforms/Transforms.cpp
-  PRIVATE_LINK_LIBS
-    LLVMSupport
-  EMBED_CAPI_LINK_LIBS
-    MLIRCAPITransforms
-)
-
 # TODO: Figure out how to put this in the test tree.
 # This should not be included in the main Python extension. However,
 # putting it into MLIRPythonTestSources along with the dialect declaration
@@ -506,7 +480,7 @@
     MLIRPythonCAPI.HeaderSources
   DECLARED_SOURCES
     MLIRPythonSources
-    MLIRPythonExtension.AllPassesRegistration
+    MLIRPythonExtension.RegisterEverything
     ${_ADDL_TEST_SOURCES}
 )
 
@@ -520,7 +494,7 @@
   INSTALL_PREFIX "python_packages/mlir_core/mlir"
   DECLARED_SOURCES
     MLIRPythonSources
-    MLIRPythonExtension.AllPassesRegistration
+    MLIRPythonExtension.RegisterEverything
     ${_ADDL_TEST_SOURCES}
   COMMON_CAPI_LINK_LIBS
     MLIRPythonCAPI
diff --git a/mlir/python/mlir/_mlir_libs/__init__.py b/mlir/python/mlir/_mlir_libs/__init__.py
--- a/mlir/python/mlir/_mlir_libs/__init__.py
+++ b/mlir/python/mlir/_mlir_libs/__init__.py
@@ -9,12 +9,6 @@
 _this_dir = os.path.dirname(__file__)
 
 
-# These submodules have no type stubs and are thus opaque to the type checker.
-_mlirConversions: Any
-_mlirTransforms: Any
-_mlirAllPassesRegistration: Any
-
-
 def get_lib_dirs() -> Sequence[str]:
   """Gets the lib directory for linking to shared libraries.
 
@@ -31,3 +25,77 @@
   not be present.
   """
   return [os.path.join(_this_dir, "include")]
+
+
+# Perform Python level site initialization. This involves:
+#   1. Attempting to load initializer modules, specific to the distribution.
+#   2. Defining the concrete mlir.ir.Context that does site specific 
+#      initialization.
+#
+# Aside from just being far more convenient to do this at the Python level,
+# it is actually quite hard/impossible to have such __init__ hooks, given
+# the pybind memory model (i.e. there is not a Python reference to the object
+# in the scope of the base class __init__).
+#
+# For #1, we:
+#   a. Probe for modules named '_mlirRegisterEverything' and 
+#     '_site_initialize_{i}', where 'i' is a number starting at zero and 
+#     proceeding so long as a module with the name is found.
+#   b. If the module has a 'register_dialects' attribute, it will be called
+#     immediately with a DialectRegistry to populate.
+#   c. If the module has a 'context_init_hook', it will be added to a list
+#     of callbacks that are invoked as the last step of Context 
+#     initialization (and passed the Context under construction).
+#
+# This facility allows downstreams to customize Context creation to their
+# needs.
+def _site_initialize():
+  import importlib
+  import itertools
+  import logging
+  from ._mlir import ir
+  registry = ir.DialectRegistry()
+  post_init_hooks = []
+
+  def process_initializer_module(module_name):
+    try:
+      m = importlib.import_module(f".{module_name}", __name__)
+    except ModuleNotFoundError:
+      return False
+
+    logging.debug("Initializing MLIR with module: %s", module_name)
+    if hasattr(m, "register_dialects"):
+      logging.debug("Registering dialects from initializer %r", m)
+      m.register_dialects(registry)
+    if hasattr(m, "context_init_hook"):
+      logging.debug("Adding context init hook from %r", m)
+      post_init_hooks.append(m.context_init_hook)
+    return True
+
+
+  # If _mlirRegisterEverything is built, then include it as an initializer
+  # module.
+  process_initializer_module("_mlirRegisterEverything")
+
+  # Load all _site_initialize_{i} modules, where 'i' is a number starting
+  # at 0.
+  for i in itertools.count():
+    module_name = f"_site_initialize_{i}"
+    if not process_initializer_module(module_name):
+      break
+
+  class Context(ir._BaseContext):
+    def __init__(self, *args, **kwargs):
+      super().__init__(*args, **kwargs)
+      self.append_dialect_registry(registry)
+      for hook in post_init_hooks:
+        hook(self)
+      # TODO: There is some debate about whether we should eagerly load
+      # all dialects. It is being done here in order to preserve existing
+      # behavior. See: https://github.com/llvm/llvm-project/issues/56037
+      self.load_all_available_dialects()
+
+  ir.Context = Context
+
+
+_site_initialize()
diff --git a/mlir/python/mlir/_mlir_libs/_mlir/ir.pyi b/mlir/python/mlir/_mlir_libs/_mlir/ir.pyi
--- a/mlir/python/mlir/_mlir_libs/_mlir/ir.pyi
+++ b/mlir/python/mlir/_mlir_libs/_mlir/ir.pyi
@@ -479,6 +479,11 @@
     def d(self) -> Dialects: ...
     @property
     def dialects(self) -> Dialects: ...
+    def append_dialect_registry(self, registry: "DialectRegistry") -> None: ...
+    def load_all_available_dialects(self) -> None: ...
+
+class DialectRegistry:
+    def __init__(self) -> None: ...
 
 # TODO: Auto-generated. Audit and fix.
 class DenseElementsAttr(Attribute):
diff --git a/mlir/python/mlir/all_passes_registration/__init__.py b/mlir/python/mlir/all_passes_registration/__init__.py
deleted file mode 100644
--- a/mlir/python/mlir/all_passes_registration/__init__.py
+++ /dev/null
@@ -1,5 +0,0 @@
-#  Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-#  See https://llvm.org/LICENSE.txt for license information.
-#  SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-from .._mlir_libs import _mlirAllPassesRegistration as _cextAllPasses
diff --git a/mlir/python/mlir/conversions/__init__.py b/mlir/python/mlir/conversions/__init__.py
deleted file mode 100644
--- a/mlir/python/mlir/conversions/__init__.py
+++ /dev/null
@@ -1,7 +0,0 @@
-#  Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-#  See https://llvm.org/LICENSE.txt for license information.
-#  SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-# Expose the corresponding C-Extension module with a well-known name at this
-# level.
-from .._mlir_libs import _mlirConversions as _cextConversions
diff --git a/mlir/python/mlir/transforms/__init__.py b/mlir/python/mlir/transforms/__init__.py
deleted file mode 100644
--- a/mlir/python/mlir/transforms/__init__.py
+++ /dev/null
@@ -1,7 +0,0 @@
-#  Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-#  See https://llvm.org/LICENSE.txt for license information.
-#  SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-# Expose the corresponding C-Extension module with a well-known name at this
-# level.
-from .._mlir_libs import _mlirTransforms as _cextTransforms
diff --git a/mlir/test/CAPI/CMakeLists.txt b/mlir/test/CAPI/CMakeLists.txt
--- a/mlir/test/CAPI/CMakeLists.txt
+++ b/mlir/test/CAPI/CMakeLists.txt
@@ -26,8 +26,8 @@
   LINK_LIBS PRIVATE
     MLIRCAPIConversion
     MLIRCAPIExecutionEngine
-    MLIRCAPIRegistration
-  )
+    MLIRCAPIRegisterEverything
+)
 endif()
 
 _add_capi_test_executable(mlir-capi-ir-test
@@ -35,7 +35,7 @@
   LINK_LIBS PRIVATE
     MLIRCAPIIR
     MLIRCAPIFunc
-    MLIRCAPIRegistration
+    MLIRCAPIRegisterEverything
 )
 
 _add_capi_test_executable(mlir-capi-llvm-test
@@ -43,7 +43,7 @@
   LINK_LIBS PRIVATE
     MLIRCAPIIR
     MLIRCAPILLVM
-    MLIRCAPIRegistration
+    MLIRCAPIRegisterEverything
 )
 
 _add_capi_test_executable(mlir-capi-pass-test
@@ -51,7 +51,7 @@
   LINK_LIBS PRIVATE
     MLIRCAPIFunc
     MLIRCAPIIR
-    MLIRCAPIRegistration
+    MLIRCAPIRegisterEverything
     MLIRCAPITransforms
 )
 
@@ -59,7 +59,7 @@
   sparse_tensor.c
   LINK_LIBS PRIVATE
     MLIRCAPIIR
-    MLIRCAPIRegistration
+    MLIRCAPIRegisterEverything
     MLIRCAPISparseTensor
 )
 
@@ -67,7 +67,7 @@
   quant.c
   LINK_LIBS PRIVATE
     MLIRCAPIIR
-    MLIRCAPIRegistration
+    MLIRCAPIRegisterEverything
     MLIRCAPIQuant
 )
 
@@ -75,6 +75,6 @@
   pdl.c
   LINK_LIBS PRIVATE
     MLIRCAPIIR
-    MLIRCAPIRegistration
+    MLIRCAPIRegisterEverything
     MLIRCAPIPDL
 )
diff --git a/mlir/test/CAPI/execution_engine.c b/mlir/test/CAPI/execution_engine.c
--- a/mlir/test/CAPI/execution_engine.c
+++ b/mlir/test/CAPI/execution_engine.c
@@ -15,7 +15,7 @@
 #include "mlir-c/Conversion.h"
 #include "mlir-c/ExecutionEngine.h"
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
+#include "mlir-c/RegisterEverything.h"
 
 #include <assert.h>
 #include <math.h>
@@ -23,6 +23,13 @@
 #include <stdlib.h>
 #include <string.h>
 
+static void registerAllUpstreamDialects(MlirContext ctx) {
+  MlirDialectRegistry registry = mlirDialectRegistryCreate();
+  mlirRegisterAllDialects(registry);
+  mlirContextAppendDialectRegistry(ctx, registry);
+  mlirDialectRegistryDestroy(registry);
+}
+
 void lowerModuleToLLVM(MlirContext ctx, MlirModule module) {
   MlirPassManager pm = mlirPassManagerCreate(ctx);
   MlirOpPassManager opm = mlirPassManagerGetNestedUnder(
@@ -41,7 +48,8 @@
 // CHECK-LABEL: Running test 'testSimpleExecution'
 void testSimpleExecution() {
   MlirContext ctx = mlirContextCreate();
-  mlirRegisterAllDialects(ctx);
+  registerAllUpstreamDialects(ctx);
+
   MlirModule module = mlirModuleCreateParse(
       ctx, mlirStringRefCreateFromCString(
                // clang-format off
diff --git a/mlir/test/CAPI/ir.c b/mlir/test/CAPI/ir.c
--- a/mlir/test/CAPI/ir.c
+++ b/mlir/test/CAPI/ir.c
@@ -18,7 +18,7 @@
 #include "mlir-c/Diagnostics.h"
 #include "mlir-c/Dialect/Func.h"
 #include "mlir-c/IntegerSet.h"
-#include "mlir-c/Registration.h"
+#include "mlir-c/RegisterEverything.h"
 #include "mlir-c/Support.h"
 
 #include <assert.h>
@@ -28,6 +28,13 @@
 #include <stdlib.h>
 #include <string.h>
 
+static void registerAllUpstreamDialects(MlirContext ctx) {
+  MlirDialectRegistry registry = mlirDialectRegistryCreate();
+  mlirRegisterAllDialects(registry);
+  mlirContextAppendDialectRegistry(ctx, registry);
+  mlirDialectRegistryDestroy(registry);
+}
+
 void populateLoopBody(MlirContext ctx, MlirBlock loopBody,
                       MlirLocation location, MlirBlock funcBody) {
   MlirValue iv = mlirBlockGetArgument(loopBody, 0);
@@ -1646,7 +1653,9 @@
   // CHECK-LABEL: @testOperands
 
   MlirContext ctx = mlirContextCreate();
-  mlirRegisterAllDialects(ctx);
+  registerAllUpstreamDialects(ctx);
+
+  mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("arith"));
   mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("test"));
   MlirLocation loc = mlirLocationUnknownGet(ctx);
   MlirType indexType = mlirIndexTypeGet(ctx);
@@ -1714,7 +1723,8 @@
   // CHECK-LABEL: @testClone
 
   MlirContext ctx = mlirContextCreate();
-  mlirRegisterAllDialects(ctx);
+  registerAllUpstreamDialects(ctx);
+
   mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("func"));
   MlirLocation loc = mlirLocationUnknownGet(ctx);
   MlirType indexType = mlirIndexTypeGet(ctx);
@@ -2036,7 +2046,12 @@
 
 int main() {
   MlirContext ctx = mlirContextCreate();
-  mlirRegisterAllDialects(ctx);
+  registerAllUpstreamDialects(ctx);
+  mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("func"));
+  mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("memref"));
+  mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("shape"));
+  mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("scf"));
+
   if (constructAndTraverseIr(ctx))
     return 1;
   buildWithInsertionsAndPrint(ctx);
diff --git a/mlir/test/CAPI/pass.c b/mlir/test/CAPI/pass.c
--- a/mlir/test/CAPI/pass.c
+++ b/mlir/test/CAPI/pass.c
@@ -13,7 +13,7 @@
 #include "mlir-c/Pass.h"
 #include "mlir-c/Dialect/Func.h"
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
+#include "mlir-c/RegisterEverything.h"
 #include "mlir-c/Transforms.h"
 
 #include <assert.h>
@@ -22,9 +22,16 @@
 #include <stdlib.h>
 #include <string.h>
 
+static void registerAllUpstreamDialects(MlirContext ctx) {
+  MlirDialectRegistry registry = mlirDialectRegistryCreate();
+  mlirRegisterAllDialects(registry);
+  mlirContextAppendDialectRegistry(ctx, registry);
+  mlirDialectRegistryDestroy(registry);
+}
+
 void testRunPassOnModule() {
   MlirContext ctx = mlirContextCreate();
-  mlirRegisterAllDialects(ctx);
+  registerAllUpstreamDialects(ctx);
 
   MlirModule module = mlirModuleCreateParse(
       ctx,
@@ -62,7 +69,7 @@
 
 void testRunPassOnNestedModule() {
   MlirContext ctx = mlirContextCreate();
-  mlirRegisterAllDialects(ctx);
+  registerAllUpstreamDialects(ctx);
 
   MlirModule module = mlirModuleCreateParse(
       ctx,
@@ -264,7 +271,7 @@
 
 void testExternalPass() {
   MlirContext ctx = mlirContextCreate();
-  mlirRegisterAllDialects(ctx);
+  registerAllUpstreamDialects(ctx);
 
   MlirModule module = mlirModuleCreateParse(
       ctx,
diff --git a/mlir/test/CAPI/sparse_tensor.c b/mlir/test/CAPI/sparse_tensor.c
--- a/mlir/test/CAPI/sparse_tensor.c
+++ b/mlir/test/CAPI/sparse_tensor.c
@@ -11,7 +11,7 @@
 
 #include "mlir-c/Dialect/SparseTensor.h"
 #include "mlir-c/IR.h"
-#include "mlir-c/Registration.h"
+#include "mlir-c/RegisterEverything.h"
 
 #include <assert.h>
 #include <math.h>
diff --git a/mlir/test/python/execution_engine.py b/mlir/test/python/execution_engine.py
--- a/mlir/test/python/execution_engine.py
+++ b/mlir/test/python/execution_engine.py
@@ -62,7 +62,6 @@
 
 
 def lowerToLLVM(module):
-  import mlir.conversions
   pm = PassManager.parse(
       "convert-complex-to-llvm,convert-memref-to-llvm,convert-func-to-llvm,reconcile-unrealized-casts")
   pm.run(module)
diff --git a/mlir/test/python/integration/dialects/linalg/opsrun.py b/mlir/test/python/integration/dialects/linalg/opsrun.py
--- a/mlir/test/python/integration/dialects/linalg/opsrun.py
+++ b/mlir/test/python/integration/dialects/linalg/opsrun.py
@@ -186,10 +186,6 @@
 
 
 def transform(module, boilerplate):
-  import mlir.conversions
-  import mlir.all_passes_registration
-  import mlir.transforms
-
   # TODO: Allow cloning functions from one module to another.
   # Atm we have to resort to string concatenation.
   ops = module.operation.regions[0].blocks[0].operations
diff --git a/mlir/test/python/lib/CMakeLists.txt b/mlir/test/python/lib/CMakeLists.txt
--- a/mlir/test/python/lib/CMakeLists.txt
+++ b/mlir/test/python/lib/CMakeLists.txt
@@ -27,7 +27,6 @@
   LINK_LIBS PUBLIC
   MLIRCAPIInterfaces
   MLIRCAPIIR
-  MLIRCAPIRegistration
   MLIRPythonTestDialect
 )
 
diff --git a/mlir/test/python/lib/PythonTestCAPI.h b/mlir/test/python/lib/PythonTestCAPI.h
--- a/mlir/test/python/lib/PythonTestCAPI.h
+++ b/mlir/test/python/lib/PythonTestCAPI.h
@@ -9,7 +9,7 @@
 #ifndef MLIR_TEST_PYTHON_LIB_PYTHONTESTCAPI_H
 #define MLIR_TEST_PYTHON_LIB_PYTHONTESTCAPI_H
 
-#include "mlir-c/Registration.h"
+#include "mlir-c/IR.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/mlir/test/python/pass_manager.py b/mlir/test/python/pass_manager.py
--- a/mlir/test/python/pass_manager.py
+++ b/mlir/test/python/pass_manager.py
@@ -33,20 +33,18 @@
 # CHECK-LABEL: TEST: testParseSuccess
 def testParseSuccess():
   with Context():
-    # A first import is expected to fail because the pass isn't registered
-    # until we import mlir.transforms
+    # An unregistered pass should not parse.
     try:
-      pm = PassManager.parse("builtin.module(func.func(print-op-stats{json=false}))")
+      pm = PassManager.parse("builtin.module(func.func(not-existing-pass{json=false}))")
       # TODO: this error should be propagate to Python but the C API does not help right now.
-      # CHECK: error: 'print-op-stats' does not refer to a registered pass or pass pipeline
+      # CHECK: error: 'not-existing-pass' does not refer to a registered pass or pass pipeline
     except ValueError as e:
-      # CHECK: ValueError exception: invalid pass pipeline 'builtin.module(func.func(print-op-stats{json=false}))'.
+      # CHECK: ValueError exception: invalid pass pipeline 'builtin.module(func.func(not-existing-pass{json=false}))'.
       log("ValueError exception:", e)
     else:
       log("Exception not produced")
 
-    # This will register the pass and round-trip should be possible now.
-    import mlir.transforms
+    # A registered pass should parse successfully.
     pm = PassManager.parse("builtin.module(func.func(print-op-stats{json=false}))")
     # CHECK: Roundtrip: builtin.module(func.func(print-op-stats{json=false}))
     log("Roundtrip: ", pm)
@@ -71,7 +69,6 @@
 def testInvalidNesting():
   with Context():
     try:
-      import mlir.all_passes_registration
       pm = PassManager.parse("func.func(normalize-memrefs)")
     except ValueError as e:
       # CHECK: Can't add pass 'NormalizeMemRefs' restricted to 'builtin.module' on a PassManager intended to run on 'func.func', did you intend to nest?
diff --git a/utils/bazel/llvm-project-overlay/mlir/BUILD.bazel b/utils/bazel/llvm-project-overlay/mlir/BUILD.bazel
--- a/utils/bazel/llvm-project-overlay/mlir/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/mlir/BUILD.bazel
@@ -384,7 +384,7 @@
         "include/mlir-c/IntegerSet.h",
         "include/mlir-c/Interfaces.h",
         "include/mlir-c/Pass.h",
-        "include/mlir-c/Registration.h",
+        "include/mlir-c/RegisterEverything.h",
         "include/mlir-c/Support.h",
         "include/mlir/CAPI/AffineExpr.h",
         "include/mlir/CAPI/AffineMap.h",
@@ -644,9 +644,9 @@
 )
 
 mlir_c_api_cc_library(
-    name = "CAPIRegistration",
-    srcs = ["lib/CAPI/Registration/Registration.cpp"],
-    hdrs = ["include/mlir-c/Registration.h"],
+    name = "CAPIRegisterEverything",
+    srcs = ["lib/CAPI/RegisterEverything/RegisterEverything.cpp"],
+    hdrs = ["include/mlir-c/RegisterEverything.h"],
     capi_deps = [
         ":CAPIIR",
     ],
@@ -744,7 +744,6 @@
         ":CAPIGPU",
         ":CAPIIR",
         ":CAPIInterfaces",
-        ":CAPIRegistration",
         ":MLIRBindingsPythonHeadersAndDeps",
         "//llvm:Support",
         "@pybind11",
diff --git a/utils/bazel/llvm-project-overlay/mlir/python/BUILD.bazel b/utils/bazel/llvm-project-overlay/mlir/python/BUILD.bazel
--- a/utils/bazel/llvm-project-overlay/mlir/python/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/mlir/python/BUILD.bazel
@@ -19,13 +19,6 @@
 # Core IR modules.
 ##---------------------------------------------------------------------------##
 
-filegroup(
-    name = "ConversionsPyFiles",
-    srcs = glob([
-        "mlir/conversions/*.py",
-    ]),
-)
-
 filegroup(
     name = "DialectCorePyFiles",
     srcs = [
@@ -83,20 +76,6 @@
     ]),
 )
 
-filegroup(
-    name = "TransformsPyFiles",
-    srcs = glob([
-        "mlir/transforms/*.py",
-    ]),
-)
-
-filegroup(
-    name = "AllPassesRegistrationPyFiles",
-    srcs = glob([
-        "mlir/all_passes_registration/*.py",
-    ]),
-)
-
 ##---------------------------------------------------------------------------##
 # Builtin dialect.
 ##---------------------------------------------------------------------------##