diff --git a/mlir/include/mlir/IR/BuiltinOps.h b/mlir/include/mlir/IR/BuiltinOps.h
--- a/mlir/include/mlir/IR/BuiltinOps.h
+++ b/mlir/include/mlir/IR/BuiltinOps.h
@@ -17,6 +17,7 @@
 #include "mlir/IR/OwningOpRef.h"
 #include "mlir/IR/SymbolTable.h"
 #include "mlir/Interfaces/CallInterfaces.h"
+#include "mlir/Interfaces/CastInterfaces.h"
 #include "llvm/Support/PointerLikeTypeTraits.h"
 
 //===----------------------------------------------------------------------===//
diff --git a/mlir/include/mlir/IR/BuiltinOps.td b/mlir/include/mlir/IR/BuiltinOps.td
--- a/mlir/include/mlir/IR/BuiltinOps.td
+++ b/mlir/include/mlir/IR/BuiltinOps.td
@@ -17,6 +17,7 @@
 include "mlir/IR/BuiltinDialect.td"
 include "mlir/IR/SymbolInterfaces.td"
 include "mlir/Interfaces/CallInterfaces.td"
+include "mlir/Interfaces/CastInterfaces.td"
 
 // Base class for Builtin dialect ops.
 class Builtin_Op<string mnemonic, list<OpTrait> traits = []> :
@@ -220,4 +221,48 @@
   let assemblyFormat = "attr-dict";
 }
 
+//===----------------------------------------------------------------------===//
+// PartialConversionCastOp
+//===----------------------------------------------------------------------===//
+
+def PartialConversionCastOp : Builtin_Op<"partial_conversion_cast", [
+    DeclareOpInterfaceMethods<CastOpInterface>
+  ]> {
+  let summary = "An operation that opaquely converts from one type to another";
+  let description = [{
+    A `partial_conversion_cast` operation represents an opaque conversion from
+    one set of types to another, that is used to enable the inter-mixing of
+    different type systems. This operation should not be attributed any special
+    representational or execution semantics, and is generally only intended to
+    be used to satisfy the temporary intermixing of type systems during the
+    conversion of one type system to another.
+
+    This operation may produce results of arity 1-N, and accept as input
+    operands of arity 0-N.
+
+    Example:
+
+    ```mlir
+    // An opaque 0-1 cast.
+    %result = partial_conversion_cast to f64
+
+    // An opaque 1-1 cast.
+    %result = partial_conversion_cast(%operand : i32) to f64
+
+    // An opaque 1-N cast.
+    %results:2 = partial_conversion_cast(%operand : i32) to i32, i32
+
+    // An opaque N-1 cast.
+    %result = partial_conversion_cast(%operand, %operand : i32, i32) to i32
+    ```
+  }];
+
+  let arguments = (ins Variadic<AnyType>:$inputs);
+  let results = (outs Variadic<AnyType>:$outputs);
+  let assemblyFormat = [{
+    (`(` $inputs^ `:` type($inputs) `)`)? `to` type($outputs) attr-dict
+  }];
+  let hasCanonicalizer = 1;
+}
+
 #endif // BUILTIN_OPS
diff --git a/mlir/lib/IR/BuiltinDialect.cpp b/mlir/lib/IR/BuiltinDialect.cpp
--- a/mlir/lib/IR/BuiltinDialect.cpp
+++ b/mlir/lib/IR/BuiltinDialect.cpp
@@ -18,6 +18,7 @@
 #include "mlir/IR/BuiltinTypes.h"
 #include "mlir/IR/FunctionImplementation.h"
 #include "mlir/IR/OpImplementation.h"
+#include "mlir/IR/PatternMatch.h"
 #include "llvm/ADT/MapVector.h"
 
 using namespace mlir;
@@ -236,6 +237,41 @@
   return success();
 }
 
+//===----------------------------------------------------------------------===//
+// PartialConversionCastOp
+//===----------------------------------------------------------------------===//
+
+namespace {
+/// Fold dead partial conversions that no longer have uses.
+/// `PartialConversionCastOp` does not provide any information about
+/// effects(purposefully to remain opaque to users), so we need an explicit
+/// canonicalization to erase it if unused.
+struct SimplifyDeadPartialConversionCastOp
+    : public OpRewritePattern<PartialConversionCastOp> {
+  using OpRewritePattern<PartialConversionCastOp>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(PartialConversionCastOp op,
+                                PatternRewriter &rewriter) const override {
+    if (op.use_empty()) {
+      rewriter.eraseOp(op);
+      return success();
+    }
+    return failure();
+  }
+};
+} // end anonymous namespace
+
+void PartialConversionCastOp::getCanonicalizationPatterns(
+    OwningRewritePatternList &results, MLIRContext *context) {
+  results.insert<SimplifyDeadPartialConversionCastOp>(context);
+}
+
+bool PartialConversionCastOp::areCastCompatible(TypeRange inputs,
+                                                TypeRange outputs) {
+  // `PartialConversionCastOp` is agnostic of the input/output types.
+  return true;
+}
+
 //===----------------------------------------------------------------------===//
 // TableGen'd op method definitions
 //===----------------------------------------------------------------------===//
diff --git a/mlir/lib/IR/CMakeLists.txt b/mlir/lib/IR/CMakeLists.txt
--- a/mlir/lib/IR/CMakeLists.txt
+++ b/mlir/lib/IR/CMakeLists.txt
@@ -37,6 +37,7 @@
   MLIRBuiltinOpsIncGen
   MLIRBuiltinTypesIncGen
   MLIRCallInterfacesIncGen
+  MLIRCastInterfacesIncGen
   MLIROpAsmInterfaceIncGen
   MLIRRegionKindInterfaceIncGen
   MLIRSymbolInterfacesIncGen
diff --git a/mlir/test/Dialect/Builtin/invalid.mlir b/mlir/test/Dialect/Builtin/invalid.mlir
new file mode 100644
--- /dev/null
+++ b/mlir/test/Dialect/Builtin/invalid.mlir
@@ -0,0 +1,7 @@
+// RUN: mlir-opt %s -split-input-file -verify-diagnostics
+
+// expected-error@+1 {{expected at least one result for cast operation}}
+"partial_conversion_cast"() : () -> ()
+
+// -----
+
diff --git a/mlir/test/Dialect/Builtin/ops.mlir b/mlir/test/Dialect/Builtin/ops.mlir
new file mode 100644
--- /dev/null
+++ b/mlir/test/Dialect/Builtin/ops.mlir
@@ -0,0 +1,19 @@
+// RUN: mlir-opt %s -allow-unregistered-dialect | mlir-opt -allow-unregistered-dialect
+
+//===----------------------------------------------------------------------===//
+// PartialConversionCastOp
+//===----------------------------------------------------------------------===//
+
+%operand = "foo.op"() : () -> i32
+
+// An opaque 0-1 cast.
+%result = partial_conversion_cast to f64
+
+// An opaque 1-1 cast.
+%result1 = partial_conversion_cast(%operand : i32) to f64
+
+// An opaque 1-N cast.
+%results2:2 = partial_conversion_cast(%operand : i32) to i32, i32
+
+// An opaque N-1 cast.
+%result3 = partial_conversion_cast(%operand, %operand : i32, i32) to i32