diff --git a/flang/include/flang/Optimizer/Dialect/FIROps.h b/flang/include/flang/Optimizer/Dialect/FIROps.h
--- a/flang/include/flang/Optimizer/Dialect/FIROps.h
+++ b/flang/include/flang/Optimizer/Dialect/FIROps.h
@@ -9,7 +9,9 @@
 #ifndef FORTRAN_OPTIMIZER_DIALECT_FIROPS_H
 #define FORTRAN_OPTIMIZER_DIALECT_FIROPS_H
 
+#include "flang/Optimizer/Dialect/FIRAttr.h"
 #include "flang/Optimizer/Dialect/FIRType.h"
+#include "flang/Optimizer/Dialect/FortranVariableInterface.h"
 #include "mlir/Dialect/Arith/IR/Arith.h"
 #include "mlir/Dialect/Func/IR/FuncOps.h"
 #include "mlir/Interfaces/LoopLikeInterface.h"
diff --git a/flang/include/flang/Optimizer/Dialect/FIROps.td b/flang/include/flang/Optimizer/Dialect/FIROps.td
--- a/flang/include/flang/Optimizer/Dialect/FIROps.td
+++ b/flang/include/flang/Optimizer/Dialect/FIROps.td
@@ -16,6 +16,9 @@
 
 include "flang/Optimizer/Dialect/FIRDialect.td"
 include "flang/Optimizer/Dialect/FIRTypes.td"
+include "flang/Optimizer/Dialect/FIRAttr.td"
+include "flang/Optimizer/Dialect/FortranVariableInterface.td"
+include "mlir/IR/BuiltinAttributes.td"
 
 // Base class for FIR operations.
 // All operations automatically get a prefix of "fir.".
@@ -2863,4 +2866,61 @@
   let results = (outs BoolLike);
 }
 
+def fir_DeclareOp : fir_Op<"declare", [AttrSizedOperandSegments,
+    DeclareOpInterfaceMethods<FortranVariableOpInterface>]> {
+  let summary = "declare a variable";
+
+  let description = [{
+    Tie the properties of a Fortran variable to an address. The properties
+    include bounds, length parameters, and Fortran attributes.
+
+    The memref argument describes the storage of the variable. It may be a
+    raw address (fir.ref<T>), or a box or class value or address (fir.box<T>,
+    fir.ref<fir.box<T>>, fir.class<T>, fir.ref<fir.class<T>>).
+
+    The shape argument encodes explicit extents and lower bounds. It must be
+    provided if the memref is the raw address of an array.
+    The shape argument must not be provided if memref operand is a box or
+    class value or address, unless the shape is a shift (encodes lower bounds)
+    and the memref if a box value (this covers assumed shapes with local lower
+    bounds).
+
+    The typeparams values are meant to carry the non-deferred length parameters
+    (this includes both Fortran assumed and explicit length parameters).
+    It must always be provided for characters and parametrized derived types
+    when memref is not a box value or address.
+
+    Example:
+
+    CHARACTER(n), OPTIONAL, TARGET :: c(10:, 20:)
+
+    Can be represented as:
+    ```
+    func.func @foo(%arg0: !fir.box<!fir.array<?x?x!fir.char<1,?>>>, %arg1: !fir.ref<i64>) {
+      %c10 = arith.constant 10 : index
+      %c20 = arith.constant 20 : index
+      %1 = fir.load %ag1 : fir.ref<i64>
+      %2 = fir.shift %c10, %c20 : (index, index) -> !fir.shift<2>
+      %3 = fir.declare %arg0(%2) typeparams %1 {fortran_attrs = #fir.var_attrs<optional, target>, uniq_name = "c"}
+      // ... uses %3 as "c"
+    }
+   ```
+  }];
+
+  let arguments = (ins
+    AnyRefOrBox:$memref,
+    Optional<AnyShapeOrShiftType>:$shape,
+    Variadic<AnyIntegerType>:$typeparams,
+    Builtin_StringAttr:$uniq_name,
+    OptionalAttr<fir_FortranVariableFlagsAttr>:$fortran_attrs
+  );
+
+  let results = (outs AnyRefOrBox);
+
+  let assemblyFormat = [{
+    $memref (`(` $shape^ `)`)? (`typeparams` $typeparams^)?
+     attr-dict `:` functional-type(operands, results)
+  }];
+}
+
 #endif
diff --git a/flang/include/flang/Optimizer/Dialect/FortranVariableInterface.td b/flang/include/flang/Optimizer/Dialect/FortranVariableInterface.td
--- a/flang/include/flang/Optimizer/Dialect/FortranVariableInterface.td
+++ b/flang/include/flang/Optimizer/Dialect/FortranVariableInterface.td
@@ -46,8 +46,8 @@
       }]
     >,
     InterfaceMethod<
-      /*desc=*/"Get the shape of the variable",
-      /*retTy=*/"llvm::Optional<mlir::Value>",
+      /*desc=*/"Get the shape of the variable. May be a null value.",
+      /*retTy=*/"mlir::Value",
       /*methodName=*/"getShape",
       /*args=*/(ins),
       /*methodBody=*/[{}],
@@ -74,7 +74,7 @@
     /// Get the sequence type or scalar value type corresponding to this
     /// variable.
     mlir::Type getElementOrSequenceType() {
-      return fir::unwrapPassByRefType(getBase().getType());
+      return fir::unwrapPassByRefType(fir::unwrapRefType(getBase().getType()));
     }
 
     /// Get the scalar value type corresponding to this variable.
@@ -87,6 +87,17 @@
       return getElementOrSequenceType().isa<fir::SequenceType>();
     }
 
+    /// Return the rank of the entity if it is known at compile time.
+    llvm::Optional<unsigned> getRank() {
+      if (auto sequenceType =
+            getElementOrSequenceType().dyn_cast<fir::SequenceType>()) {
+        if (sequenceType.hasUnknownShape())
+          return {};
+        return sequenceType.getDimension();
+      }
+      return 0;
+    }
+
     /// Is this variable a Fortran pointer ?
     bool isPointer() {
       auto attrs = getFortranAttrs();
@@ -117,8 +128,32 @@
       return getExplicitTypeParams()[0];
     }
 
+    /// Is this variable represented as a fir.box or fir.class value ?
+    bool isBoxValue() {
+      return getBase().getType().isa<fir::BaseBoxType>();
+    }
+
+    /// Is this variable represented as a fir.box or fir.class address ?
+    bool isBoxAddress() {
+      mlir::Type type = getBase().getType();
+      return fir::isa_ref_type(type) &&
+         fir::unwrapRefType(type).isa<fir::BaseBoxType>();
+    }
+
+    /// Is this variable represented as the value or address of a fir.box or
+    /// fir.class ?
+    bool isBox() {
+      return fir::unwrapRefType(getBase().getType()).isa<fir::BaseBoxType>();
+    }
+
+    /// Interface verifier imlementation.
+    mlir::LogicalResult verifyImpl();
+
   }];
 
+  let verify = [{
+    return ::mlir::cast<::fir::FortranVariableOpInterface>($_op).verifyImpl();
+  }];
 }
 
 #endif  // FORTRANVARIABLEINTERFACE
diff --git a/flang/lib/Optimizer/Dialect/FortranVariableInterface.cpp b/flang/lib/Optimizer/Dialect/FortranVariableInterface.cpp
--- a/flang/lib/Optimizer/Dialect/FortranVariableInterface.cpp
+++ b/flang/lib/Optimizer/Dialect/FortranVariableInterface.cpp
@@ -15,3 +15,52 @@
 namespace fir {
 #include "flang/Optimizer/Dialect/FortranVariableInterface.cpp.inc"
 }
+
+mlir::LogicalResult fir::FortranVariableOpInterface::verifyImpl() {
+  const unsigned numExplicitTypeParams = getExplicitTypeParams().size();
+  if (isCharacter()) {
+    if (numExplicitTypeParams > 1)
+      return emitOpError(
+          "of character entity must have at most one length parameter");
+    if (numExplicitTypeParams == 0 && !isBox())
+      return emitOpError("must be provided exactly one type parameter when its "
+                         "base is a character that is not a box");
+
+  } else if (auto recordType = getElementType().dyn_cast<fir::RecordType>()) {
+    if (numExplicitTypeParams < recordType.getNumLenParams() && !isBox())
+      return emitOpError("must be provided all the derived type length "
+                         "parameters when the base is not a box");
+    if (numExplicitTypeParams > recordType.getNumLenParams())
+      return emitOpError("has too many length parameters");
+  } else if (numExplicitTypeParams != 0) {
+    return emitOpError("of numeric, logical, or assumed type entity must not "
+                       "have length parameters");
+  }
+
+  if (isArray()) {
+    if (mlir::Value shape = getShape()) {
+      if (isBoxAddress())
+        return emitOpError("for box address must not have a shape operand");
+      unsigned shapeRank = 0;
+      if (auto shapeType = shape.getType().dyn_cast<fir::ShapeType>()) {
+        shapeRank = shapeType.getRank();
+      } else if (auto shapeShiftType =
+                     shape.getType().dyn_cast<fir::ShapeShiftType>()) {
+        shapeRank = shapeShiftType.getRank();
+      } else {
+        if (!isBoxValue())
+          emitOpError("of array entity with a raw address base must have a "
+                      "shape operand that is a shape or shapeshift");
+        shapeRank = shape.getType().cast<fir::ShiftType>().getRank();
+      }
+
+      llvm::Optional<unsigned> rank = getRank();
+      if (!rank || *rank != shapeRank)
+        return emitOpError("has conflicting shape and base operand ranks");
+    } else if (!isBox()) {
+      emitOpError("of array entity with a raw address base must have a shape "
+                  "operand that is a shape or shapeshift");
+    }
+  }
+  return mlir::success();
+}
diff --git a/flang/test/Fir/declare.fir b/flang/test/Fir/declare.fir
new file mode 100644
--- /dev/null
+++ b/flang/test/Fir/declare.fir
@@ -0,0 +1,145 @@
+// Test fir.declare operation parse, verify (no errors), and unparse.
+
+// RUN: fir-opt %s | fir-opt | FileCheck %s
+
+func.func @numeric_declare(%arg0: !fir.ref<f32>) {
+  %0 = fir.declare %arg0 {uniq_name = "x"} : (!fir.ref<f32>) -> !fir.ref<f32>
+  return
+}
+// CHECK-LABEL:   func.func @numeric_declare(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<f32>) {
+// CHECK:  %[[VAL_1:.*]] = fir.declare %[[VAL_0]] {uniq_name = "x"} : (!fir.ref<f32>) -> !fir.ref<f32>
+
+
+func.func @char_declare(%arg0: !fir.boxchar<1> ) {
+  %0:2 = fir.unboxchar %arg0 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+  %1 = fir.declare %0#0 typeparams %0#1 {uniq_name = "c"} : (!fir.ref<!fir.char<1,?>>, index) -> !fir.ref<!fir.char<1,?>>
+  return
+}
+// CHECK-LABEL:   func.func @char_declare(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.boxchar<1>) {
+// CHECK:  %[[VAL_1:.*]]:2 = fir.unboxchar %[[VAL_0]] : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+// CHECK:  %[[VAL_2:.*]] = fir.declare %[[VAL_1]]#0 typeparams %[[VAL_1]]#1 {uniq_name = "c"} : (!fir.ref<!fir.char<1,?>>, index) -> !fir.ref<!fir.char<1,?>>
+
+
+func.func @derived_declare(%arg0: !fir.ref<!fir.type<t{field:i32}>>) {
+  %0 = fir.declare %arg0 {uniq_name = "x"} : (!fir.ref<!fir.type<t{field:i32}>>) -> !fir.ref<!fir.type<t{field:i32}>>
+  return
+}
+// CHECK-LABEL:   func.func @derived_declare(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<!fir.type<t{field:i32}>>) {
+// CHECK:  %[[VAL_1:.*]] = fir.declare %[[VAL_0]] {uniq_name = "x"} : (!fir.ref<!fir.type<t{field:i32}>>) -> !fir.ref<!fir.type<t{field:i32}>>
+
+
+func.func @pdt_declare(%arg0: !fir.ref<!fir.type<pdt(param:i32){field:i32}>>) {
+  %c1 = arith.constant 1 : index
+  %0 = fir.declare %arg0 typeparams %c1 {uniq_name = "x"} : (!fir.ref<!fir.type<pdt(param:i32){field:i32}>>, index) -> !fir.ref<!fir.type<pdt(param:i32){field:i32}>>
+  return
+}
+// CHECK-LABEL:   func.func @pdt_declare(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<!fir.type<pdt(param:i32){field:i32}>>) {
+// CHECK:  %[[VAL_1:.*]] = arith.constant 1 : index
+// CHECK:  %[[VAL_2:.*]] = fir.declare %[[VAL_0]] typeparams %[[VAL_1]] {uniq_name = "x"} : (!fir.ref<!fir.type<pdt(param:i32){field:i32}>>, index) -> !fir.ref<!fir.type<pdt(param:i32){field:i32}>>
+
+
+func.func @array_declare(%arg0: !fir.ref<!fir.array<?x?xf32>>) {
+  %c1 = arith.constant 1 : index
+  %c2 = arith.constant 2 : index
+  %shape = fir.shape %c1, %c2 : (index, index) -> !fir.shape<2>
+  %0 = fir.declare %arg0(%shape) {uniq_name = "x"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shape<2>) -> !fir.ref<!fir.array<?x?xf32>>
+  return
+}
+// CHECK-LABEL:   func.func @array_declare(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<!fir.array<?x?xf32>>) {
+// CHECK:  %[[VAL_1:.*]] = arith.constant 1 : index
+// CHECK:  %[[VAL_2:.*]] = arith.constant 2 : index
+// CHECK:  %[[VAL_3:.*]] = fir.shape %[[VAL_1]], %[[VAL_2]] : (index, index) -> !fir.shape<2>
+// CHECK:  %[[VAL_4:.*]] = fir.declare %[[VAL_0]](%[[VAL_3]]) {uniq_name = "x"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shape<2>) -> !fir.ref<!fir.array<?x?xf32>>
+
+
+func.func @array_declare_2(%arg0: !fir.ref<!fir.array<?x?xf32>>) {
+  %c1 = arith.constant 1 : index
+  %c2 = arith.constant 2 : index
+  %c3 = arith.constant 3 : index
+  %c4 = arith.constant 4 : index
+  %shape = fir.shape_shift %c1, %c2, %c3, %c4 : (index, index, index, index) -> !fir.shapeshift<2>
+  %0 = fir.declare %arg0(%shape) {uniq_name = "x"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shapeshift<2>) -> !fir.ref<!fir.array<?x?xf32>>
+  return
+}
+// CHECK-LABEL:   func.func @array_declare_2(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<!fir.array<?x?xf32>>) {
+// CHECK:  %[[VAL_1:.*]] = arith.constant 1 : index
+// CHECK:  %[[VAL_2:.*]] = arith.constant 2 : index
+// CHECK:  %[[VAL_3:.*]] = arith.constant 3 : index
+// CHECK:  %[[VAL_4:.*]] = arith.constant 4 : index
+// CHECK:  %[[VAL_5:.*]] = fir.shape_shift %[[VAL_1]], %[[VAL_2]], %[[VAL_3]], %[[VAL_4]] : (index, index, index, index) -> !fir.shapeshift<2>
+// CHECK:  %[[VAL_6:.*]] = fir.declare %[[VAL_0]](%[[VAL_5]]) {uniq_name = "x"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shapeshift<2>) -> !fir.ref<!fir.array<?x?xf32>>
+
+
+func.func @array_declare_box(%arg0: !fir.box<!fir.array<?x?xf32>>) {
+  %c1 = arith.constant 1 : index
+  %c2 = arith.constant 2 : index
+  %shape = fir.shift %c1, %c2 : (index, index) -> !fir.shift<2>
+  %0 = fir.declare %arg0(%shape) {uniq_name = "x"} : (!fir.box<!fir.array<?x?xf32>>, !fir.shift<2>) -> !fir.box<!fir.array<?x?xf32>>
+  return
+}
+// CHECK-LABEL:   func.func @array_declare_box(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.box<!fir.array<?x?xf32>>) {
+// CHECK:  %[[VAL_1:.*]] = arith.constant 1 : index
+// CHECK:  %[[VAL_2:.*]] = arith.constant 2 : index
+// CHECK:  %[[VAL_3:.*]] = fir.shift %[[VAL_1]], %[[VAL_2]] : (index, index) -> !fir.shift<2>
+// CHECK:  %[[VAL_4:.*]] = fir.declare %[[VAL_0]](%[[VAL_3]]) {uniq_name = "x"} : (!fir.box<!fir.array<?x?xf32>>, !fir.shift<2>) -> !fir.box<!fir.array<?x?xf32>>
+
+
+func.func @array_declare_char_box(%arg0: !fir.box<!fir.array<?x?x!fir.char<1,?>>>) {
+  %0 = fir.declare %arg0 {uniq_name = "x"} : (!fir.box<!fir.array<?x?x!fir.char<1,?>>>) -> !fir.box<!fir.array<?x?x!fir.char<1,?>>>
+  return
+}
+// CHECK-LABEL:   func.func @array_declare_char_box(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.box<!fir.array<?x?x!fir.char<1,?>>>) {
+// CHECK:  %[[VAL_1:.*]] = fir.declare %[[VAL_0]] {uniq_name = "x"} : (!fir.box<!fir.array<?x?x!fir.char<1,?>>>) -> !fir.box<!fir.array<?x?x!fir.char<1,?>>>
+
+
+func.func @array_declare_char_box_2(%arg0: !fir.box<!fir.array<?x?x!fir.char<1,?>>>) {
+  %c1 = arith.constant 1 : index
+  %c2 = arith.constant 2 : index
+  %c3 = arith.constant 3 : index
+  %shape = fir.shift %c1, %c2 : (index, index) -> !fir.shift<2>
+  %0 = fir.declare %arg0(%shape) typeparams %c3 {uniq_name = "x"} : (!fir.box<!fir.array<?x?x!fir.char<1,?>>>, !fir.shift<2>, index) -> !fir.box<!fir.array<?x?x!fir.char<1,?>>>
+  return
+}
+// CHECK-LABEL:   func.func @array_declare_char_box_2(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.box<!fir.array<?x?x!fir.char<1,?>>>) {
+// CHECK:  %[[VAL_1:.*]] = arith.constant 1 : index
+// CHECK:  %[[VAL_2:.*]] = arith.constant 2 : index
+// CHECK:  %[[VAL_3:.*]] = arith.constant 3 : index
+// CHECK:  %[[VAL_4:.*]] = fir.shift %[[VAL_1]], %[[VAL_2]] : (index, index) -> !fir.shift<2>
+// CHECK:  %[[VAL_5:.*]] = fir.declare %[[VAL_0]](%[[VAL_4]]) typeparams %[[VAL_3]] {uniq_name = "x"} : (!fir.box<!fir.array<?x?x!fir.char<1,?>>>, !fir.shift<2>, index) -> !fir.box<!fir.array<?x?x!fir.char<1,?>>>
+
+
+func.func @array_declare_char_boxaddr(%arg0: !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>) {
+  %0 = fir.declare %arg0 {uniq_name = "x"} : (!fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>) -> !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>
+  return
+}
+// CHECK-LABEL: func.func @array_declare_char_boxaddr(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>) {
+// CHECK:  %[[VAL_1:.*]] = fir.declare %[[VAL_0]] {uniq_name = "x"} : (!fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>) -> !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>
+
+
+func.func @array_declare_char_boxaddr_2(%arg0: !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>) {
+  %c3 = arith.constant 3 : index
+  %0 = fir.declare %arg0 typeparams %c3 {uniq_name = "x"} : (!fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>, index) -> !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>
+  return
+}
+// CHECK-LABEL: func.func @array_declare_char_boxaddr_2(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>) {
+// CHECK:  %[[VAL_1:.*]] = arith.constant 3 : index
+// CHECK:  %[[VAL_2:.*]] = fir.declare %[[VAL_0]] typeparams %[[VAL_1]] {uniq_name = "x"} : (!fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>, index) -> !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>
+
+func.func @array_declare_unlimited_polymorphic_boxaddr(%arg0: !fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>) {
+  %0 = fir.declare %arg0 {uniq_name = "x"} : (!fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>) -> !fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>
+  return
+}
+// CHECK-LABEL: func.func @array_declare_unlimited_polymorphic_boxaddr(
+// CHECK-SAME:    %[[VAL_0:.*]]: !fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>) {
+// CHECK:  %[[VAL_1:.*]] = fir.declare %[[VAL_0]] {uniq_name = "x"} : (!fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>) -> !fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>
diff --git a/flang/test/Fir/invalid.fir b/flang/test/Fir/invalid.fir
--- a/flang/test/Fir/invalid.fir
+++ b/flang/test/Fir/invalid.fir
@@ -808,3 +808,123 @@
   // expected-error@+1 {{Unknown fortran variable attribute: volatypo}}
   %0 = fir.alloca f32 {fortran_attrs = #fir.var_attrs<volatypo>}
 }
+
+// -----
+func.func @bad_numeric_declare(%arg0: !fir.ref<f32>) {
+  %c1 = arith.constant 1 : index
+  // expected-error@+1 {{'fir.declare' op requires attribute 'uniq_name'}}
+  %0 = fir.declare %arg0 typeparams %c1 {uniq_typo = "x"} : (!fir.ref<f32>, index) -> !fir.ref<f32>
+  return
+}
+
+// -----
+func.func @bad_numeric_declare(%arg0: !fir.ref<f32>) {
+  %c1 = arith.constant 1 : index
+  // expected-error@+1 {{'fir.declare' op of numeric, logical, or assumed type entity must not have length parameters}}
+  %0 = fir.declare %arg0 typeparams %c1 {uniq_name = "x"} : (!fir.ref<f32>, index) -> !fir.ref<f32>
+  return
+}
+
+// -----
+func.func @bad_char_declare(%arg0: !fir.boxchar<1> ) {
+  %0:2 = fir.unboxchar %arg0 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+  // expected-error@+1 {{'fir.declare' op must be provided exactly one type parameter when its base is a character that is not a box}}
+  %1 = fir.declare %0#0 {uniq_name = "c"} : (!fir.ref<!fir.char<1,?>>) -> !fir.ref<!fir.char<1,?>>
+  return
+}
+
+// -----
+func.func @bad_char_declare(%arg0: !fir.boxchar<1> ) {
+  %0:2 = fir.unboxchar %arg0 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+  // expected-error@+1 {{'fir.declare' op of character entity must have at most one length parameter}}
+  %1 = fir.declare %0#0 typeparams %0#1, %0#1 {uniq_name = "c"} : (!fir.ref<!fir.char<1,?>>, index, index) -> !fir.ref<!fir.char<1,?>>
+  return
+}
+
+// -----
+func.func @bad_derived_declare(%arg0: !fir.ref<!fir.type<t{field:i32}>>) {
+  %c1 = arith.constant 1 : index
+  // expected-error@+1 {{'fir.declare' op has too many length parameters}}
+  %0 = fir.declare %arg0 typeparams %c1 {uniq_name = "x"} : (!fir.ref<!fir.type<t{field:i32}>>, index) -> !fir.ref<!fir.type<t{field:i32}>>
+  return
+}
+
+// -----
+func.func @bad_pdt_declare(%arg0: !fir.ref<!fir.type<pdt(param:i32){field:i32}>>) {
+  // expected-error@+1 {{'fir.declare' op must be provided all the derived type length parameters when the base is not a box}}
+  %0 = fir.declare %arg0 {uniq_name = "x"} : (!fir.ref<!fir.type<pdt(param:i32){field:i32}>>) -> !fir.ref<!fir.type<pdt(param:i32){field:i32}>>
+  return
+}
+
+// -----
+func.func @bad_pdt_declare_2(%arg0: !fir.ref<!fir.type<pdt(param:i32){field:i32}>>) {
+  %c1 = arith.constant 1 : index
+  // expected-error@+1 {{'fir.declare' op has too many length parameters}}
+  %0 = fir.declare %arg0 typeparams %c1, %c1 {uniq_name = "x"} : (!fir.ref<!fir.type<pdt(param:i32){field:i32}>>, index, index) -> !fir.ref<!fir.type<pdt(param:i32){field:i32}>>
+  return
+}
+
+
+// -----
+func.func @bad_array_declare(%arg0: !fir.ref<!fir.array<?x?xf32>>) {
+  // expected-error@+1 {{'fir.declare' op of array entity with a raw address base must have a shape operand that is a shape or shapeshift}}
+  %0 = fir.declare %arg0 {uniq_name = "x"} : (!fir.ref<!fir.array<?x?xf32>>) -> !fir.ref<!fir.array<?x?xf32>>
+  return
+}
+
+// -----
+func.func @bad_array_declare_2(%arg0: !fir.ref<!fir.array<?x?xf32>>) {
+  %c1 = arith.constant 1 : index
+  %c2 = arith.constant 2 : index
+  %shift = fir.shift %c1, %c2 : (index, index) -> !fir.shift<2>
+  // expected-error@+1 {{'fir.declare' op of array entity with a raw address base must have a shape operand that is a shape or shapeshift}}
+  %0 = fir.declare %arg0(%shift) {uniq_name = "x"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shift<2>) -> !fir.ref<!fir.array<?x?xf32>>
+  return
+}
+
+// -----
+func.func @bad_array_declare_3(%arg0: !fir.ref<!fir.array<?x?xf32>>) {
+  %c1 = arith.constant 1 : index
+  %shape = fir.shape %c1 : (index) -> !fir.shape<1>
+  // expected-error@+1 {{'fir.declare' op has conflicting shape and base operand ranks}}
+  %0 = fir.declare %arg0(%shape) {uniq_name = "x"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shape<1>) -> !fir.ref<!fir.array<?x?xf32>>
+  return
+}
+
+// -----
+func.func @bad_array_declare_4(%arg0: !fir.ref<!fir.array<?x?xf32>>) {
+  %c1 = arith.constant 1 : index
+  %shape = fir.shape_shift %c1, %c1 : (index, index) -> !fir.shapeshift<1>
+  // expected-error@+1 {{'fir.declare' op has conflicting shape and base operand ranks}}
+  %0 = fir.declare %arg0(%shape) {uniq_name = "x"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shapeshift<1>) -> !fir.ref<!fir.array<?x?xf32>>
+  return
+}
+
+// -----
+func.func @bad_array_declare_box(%arg0: !fir.box<!fir.array<?x?xf32>>) {
+  %c1 = arith.constant 1 : index
+  %shape = fir.shift %c1 : (index) -> !fir.shift<1>
+  // expected-error@+1 {{'fir.declare' op has conflicting shape and base operand ranks}}
+  %0 = fir.declare %arg0(%shape) {uniq_name = "x"} : (!fir.box<!fir.array<?x?xf32>>, !fir.shift<1>) -> !fir.box<!fir.array<?x?xf32>>
+  return
+}
+
+// -----
+func.func @bad_array_declare_char_boxaddr(%arg0: !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>) {
+  %c1 = arith.constant 1 : index
+  %c2 = arith.constant 2 : index
+  %shape = fir.shift %c1, %c2 : (index, index) -> !fir.shift<2>
+  // expected-error@+1 {{'fir.declare' op for box address must not have a shape operand}}
+  %0 = fir.declare %arg0(%shape) {uniq_name = "x"} : (!fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>, !fir.shift<2>) -> !fir.ref<!fir.box<!fir.ptr<!fir.array<?x?x!fir.char<1,?>>>>>
+  return
+}
+
+// -----
+func.func @bad_array_declare_unlimited_polymorphic_boxaddr(%arg0: !fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>) {
+  %c1 = arith.constant 1 : index
+  %c2 = arith.constant 2 : index
+  %shape = fir.shift %c1, %c2 : (index, index) -> !fir.shift<2>
+  // expected-error@+1 {{'fir.declare' op for box address must not have a shape operand}}
+  %0 = fir.declare %arg0(%shape) {uniq_name = "x"} : (!fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>, !fir.shift<2>) -> !fir.ref<!fir.class<!fir.ptr<!fir.array<?x?xnone>>>>
+  return
+}
diff --git a/flang/unittests/Optimizer/CMakeLists.txt b/flang/unittests/Optimizer/CMakeLists.txt
--- a/flang/unittests/Optimizer/CMakeLists.txt
+++ b/flang/unittests/Optimizer/CMakeLists.txt
@@ -24,6 +24,7 @@
   Builder/Runtime/TransformationalTest.cpp
   FIRContextTest.cpp
   FIRTypesTest.cpp
+  FortranVariableTest.cpp
   InternalNamesTest.cpp
   KindMappingTest.cpp
   RTBuilder.cpp
diff --git a/flang/unittests/Optimizer/FortranVariableTest.cpp b/flang/unittests/Optimizer/FortranVariableTest.cpp
new file mode 100644
--- /dev/null
+++ b/flang/unittests/Optimizer/FortranVariableTest.cpp
@@ -0,0 +1,151 @@
+//===- FortranVariableTest.cpp --------------------------------------------===//
+//
+// 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 "gtest/gtest.h"
+#include "flang/Optimizer/Dialect/FIROps.h"
+#include "flang/Optimizer/Support/InitFIR.h"
+
+struct FortranVariableTest : public testing::Test {
+public:
+  void SetUp() {
+    fir::support::loadDialects(context);
+    builder = std::make_unique<mlir::OpBuilder>(&context);
+    mlir::Location loc = builder->getUnknownLoc();
+
+    // Set up a Module with a dummy function operation inside.
+    // Set the insertion point in the function entry block.
+    mlir::ModuleOp mod = builder->create<mlir::ModuleOp>(loc);
+    mlir::func::FuncOp func =
+        mlir::func::FuncOp::create(loc, "fortran_variable_tests",
+            builder->getFunctionType(llvm::None, llvm::None));
+    auto *entryBlock = func.addEntryBlock();
+    mod.push_back(mod);
+    builder->setInsertionPointToStart(entryBlock);
+  }
+
+  mlir::Location getLoc() { return builder->getUnknownLoc(); }
+  mlir::Value createConstant(std::int64_t cst) {
+    mlir::Type indexType = builder->getIndexType();
+    return builder->create<mlir::arith::ConstantOp>(
+        getLoc(), indexType, builder->getIntegerAttr(indexType, cst));
+  }
+
+  mlir::Value createShape(llvm::ArrayRef<mlir::Value> extents) {
+    mlir::Type shapeType = fir::ShapeType::get(&context, extents.size());
+    return builder->create<fir::ShapeOp>(getLoc(), shapeType, extents);
+  }
+  mlir::MLIRContext context;
+  std::unique_ptr<mlir::OpBuilder> builder;
+};
+
+TEST_F(FortranVariableTest, SimpleScalar) {
+  mlir::Location loc = getLoc();
+  mlir::Type eleType = mlir::FloatType::getF32(&context);
+  mlir::Value addr = builder->create<fir::AllocaOp>(loc, eleType);
+  auto name = mlir::StringAttr::get(&context, "x");
+  auto declare = builder->create<fir::DeclareOp>(loc, addr.getType(), addr,
+      /*shape=*/mlir::Value{}, /*typeParams=*/llvm::None, name,
+      /*fortran_attrs=*/fir::FortranVariableFlagsAttr{});
+
+  fir::FortranVariableOpInterface fortranVariable = declare;
+  EXPECT_FALSE(fortranVariable.isArray());
+  EXPECT_FALSE(fortranVariable.isCharacter());
+  EXPECT_FALSE(fortranVariable.isPointer());
+  EXPECT_FALSE(fortranVariable.isAllocatable());
+  EXPECT_FALSE(fortranVariable.hasExplicitCharLen());
+  EXPECT_EQ(fortranVariable.getElementType(), eleType);
+  EXPECT_EQ(fortranVariable.getElementOrSequenceType(),
+      fortranVariable.getElementType());
+  EXPECT_NE(fortranVariable.getBase(), addr);
+  EXPECT_EQ(fortranVariable.getBase().getType(), addr.getType());
+}
+
+TEST_F(FortranVariableTest, CharacterScalar) {
+  mlir::Location loc = getLoc();
+  mlir::Type eleType = fir::CharacterType::getUnknownLen(&context, 4);
+  mlir::Value len = createConstant(42);
+  llvm::SmallVector<mlir::Value> typeParams{len};
+  mlir::Value addr = builder->create<fir::AllocaOp>(
+      loc, eleType, /*pinned=*/false, typeParams);
+  auto name = mlir::StringAttr::get(&context, "x");
+  auto declare = builder->create<fir::DeclareOp>(loc, addr.getType(), addr,
+      /*shape=*/mlir::Value{}, typeParams, name,
+      /*fortran_attrs=*/fir::FortranVariableFlagsAttr{});
+
+  fir::FortranVariableOpInterface fortranVariable = declare;
+  EXPECT_FALSE(fortranVariable.isArray());
+  EXPECT_TRUE(fortranVariable.isCharacter());
+  EXPECT_FALSE(fortranVariable.isPointer());
+  EXPECT_FALSE(fortranVariable.isAllocatable());
+  EXPECT_TRUE(fortranVariable.hasExplicitCharLen());
+  EXPECT_EQ(fortranVariable.getElementType(), eleType);
+  EXPECT_EQ(fortranVariable.getElementOrSequenceType(),
+      fortranVariable.getElementType());
+  EXPECT_NE(fortranVariable.getBase(), addr);
+  EXPECT_EQ(fortranVariable.getBase().getType(), addr.getType());
+  EXPECT_EQ(fortranVariable.getExplicitCharLen(), len);
+}
+
+TEST_F(FortranVariableTest, SimpleArray) {
+  mlir::Location loc = getLoc();
+  mlir::Type eleType = mlir::FloatType::getF32(&context);
+  llvm::SmallVector<mlir::Value> extents{
+      createConstant(10), createConstant(20), createConstant(30)};
+  fir::SequenceType::Shape typeShape(
+      extents.size(), fir::SequenceType::getUnknownExtent());
+  mlir::Type seqTy = fir::SequenceType::get(typeShape, eleType);
+  mlir::Value addr = builder->create<fir::AllocaOp>(
+      loc, seqTy, /*pinned=*/false, /*typeParams=*/llvm::None, extents);
+  mlir::Value shape = createShape(extents);
+  auto name = mlir::StringAttr::get(&context, "x");
+  auto declare = builder->create<fir::DeclareOp>(loc, addr.getType(), addr,
+      shape, /*typeParams*/ llvm::None, name,
+      /*fortran_attrs=*/fir::FortranVariableFlagsAttr{});
+
+  fir::FortranVariableOpInterface fortranVariable = declare;
+  EXPECT_TRUE(fortranVariable.isArray());
+  EXPECT_FALSE(fortranVariable.isCharacter());
+  EXPECT_FALSE(fortranVariable.isPointer());
+  EXPECT_FALSE(fortranVariable.isAllocatable());
+  EXPECT_FALSE(fortranVariable.hasExplicitCharLen());
+  EXPECT_EQ(fortranVariable.getElementType(), eleType);
+  EXPECT_EQ(fortranVariable.getElementOrSequenceType(), seqTy);
+  EXPECT_NE(fortranVariable.getBase(), addr);
+  EXPECT_EQ(fortranVariable.getBase().getType(), addr.getType());
+}
+
+TEST_F(FortranVariableTest, CharacterArray) {
+  mlir::Location loc = getLoc();
+  mlir::Type eleType = fir::CharacterType::getUnknownLen(&context, 4);
+  mlir::Value len = createConstant(42);
+  llvm::SmallVector<mlir::Value> typeParams{len};
+  llvm::SmallVector<mlir::Value> extents{
+      createConstant(10), createConstant(20), createConstant(30)};
+  fir::SequenceType::Shape typeShape(
+      extents.size(), fir::SequenceType::getUnknownExtent());
+  mlir::Type seqTy = fir::SequenceType::get(typeShape, eleType);
+  mlir::Value addr = builder->create<fir::AllocaOp>(
+      loc, seqTy, /*pinned=*/false, typeParams, extents);
+  mlir::Value shape = createShape(extents);
+  auto name = mlir::StringAttr::get(&context, "x");
+  auto declare = builder->create<fir::DeclareOp>(loc, addr.getType(), addr,
+      shape, typeParams, name,
+      /*fortran_attrs=*/fir::FortranVariableFlagsAttr{});
+
+  fir::FortranVariableOpInterface fortranVariable = declare;
+  EXPECT_TRUE(fortranVariable.isArray());
+  EXPECT_TRUE(fortranVariable.isCharacter());
+  EXPECT_FALSE(fortranVariable.isPointer());
+  EXPECT_FALSE(fortranVariable.isAllocatable());
+  EXPECT_TRUE(fortranVariable.hasExplicitCharLen());
+  EXPECT_EQ(fortranVariable.getElementType(), eleType);
+  EXPECT_EQ(fortranVariable.getElementOrSequenceType(), seqTy);
+  EXPECT_NE(fortranVariable.getBase(), addr);
+  EXPECT_EQ(fortranVariable.getBase().getType(), addr.getType());
+  EXPECT_EQ(fortranVariable.getExplicitCharLen(), len);
+}