diff --git a/flang/include/flang/Optimizer/HLFIR/HLFIROps.td b/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
index 792cfe1d005a9..de21464ae79ce 100644
--- a/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
+++ b/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
@@ -939,7 +939,7 @@ def hlfir_RegionAssignOp : hlfir_Op<"region_assign", [hlfir_OrderedAssignmentTre
 }
 
 def hlfir_YieldOp : hlfir_Op<"yield", [Terminator, ParentOneOf<["RegionAssignOp",
-    "ElementalAddrOp", "ForallOp"]>,
+    "ElementalAddrOp", "ForallOp", "ForallMaskOp", "WhereOp", "ElseWhereOp"]>,
     SingleBlockImplicitTerminator<"fir::FirEndOp">]> {
 
   let summary = "Yield a value or variable inside a forall, where or region assignment";
@@ -1114,4 +1114,123 @@ def hlfir_ForallOp : hlfir_Op<"forall", [hlfir_OrderedAssignmentTreeOpInterface]
   }];
 }
 
+/// Shared definition for hlfir.forall_mask and hlfir.where
+/// that have the same structure and assembly format, but not the same
+/// constraints.
+class hlfir_AssignmentMaskOp<string mnemonic> : hlfir_Op<mnemonic,
+    [hlfir_OrderedAssignmentTreeOpInterface]> {
+  let regions = (region  SizedRegion<1>:$mask_region,
+                         SizedRegion<1>:$body);
+
+  let extraClassDeclaration = [{
+    void getLeafRegions(llvm::SmallVectorImpl<mlir::Region*>& regions) {
+      regions.push_back(&getMaskRegion());
+    }
+    mlir::Region* getSubTreeRegion() { return &getBody(); }
+  }];
+
+  let assemblyFormat = [{
+    $mask_region
+    attr-dict `do`
+    custom<AssignmentMaskOpBody>($body)
+  }];
+}
+
+def hlfir_ForallMaskOp : hlfir_AssignmentMaskOp<"forall_mask"> {
+  let summary = "Represent a Fortran forall mask";
+  let description = [{
+    Fortran Forall can have a scalar mask expression that depends on the
+    Forall index-name value.
+    hlfir.forall_mask allows representing this mask. The expression
+    evaluation is held in the mask region that must yield an i1 scalar
+    value.
+    An hlfir.forall_mask must be directly nested in the body region of
+    an hlfir.forall. It is a separate operation so that it can use the
+    index SSA value defined by the hlfir.forall body region.
+
+    Example: "FORALL(I=1:10, SOME_CONDITION(I)) X(I) = FOO(I)"
+    ```
+    hlfir.forall lb {
+      hlfir.yield %c1 : index
+    } ub {
+      hlfir.yield %c10 : index
+    } (%i : index) {
+      hlfir.forall_mask {
+        %mask = fir.call @some_condition(%i) : (index) -> i1
+        hlfir.yield %mask : i1
+      } do {
+        hlfir.region_assign {
+          %res = fir.call @foo(%i) : (index) -> f32
+          hlfir.yield %res : f32
+        } to {
+          %xi = hlfir.designate %x(%i) : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+          hlfir.yield %xi : !fir.ref<f32>
+        }
+      }
+    }
+    ```
+  }];
+  let hasVerifier = 1;
+}
+
+def hlfir_WhereOp : hlfir_AssignmentMaskOp<"where"> {
+  let summary = "Represent a Fortran where construct or statement";
+  let description = [{
+    Represent Fortran "where" construct or statement. The mask
+    expression evaluation is held in the mask region that must yield
+    logical array that has the same shape as all the nested
+    hlfir.region_assign left-hand sides, and all the nested hlfir.where
+    or hlfir.elsewhere masks.
+
+    The values of the where and elsewhere masks form a control mask that
+    controls all the nested hlfir.region_assign: only the array element for
+    which the related control mask value is true are assigned. Any right-hand
+    side elemental expression is only evaluated for elements where the control
+    mask is true. See Fortran standard 2018 section 10.2.3 for more detailed
+    about the control mask semantic.
+
+    An hlfir.where must not contain any hlfir.forall but it may be contained
+    in such operation. This matches Fortran rules.
+  }];
+  let hasVerifier = 1;
+}
+
+def hlfir_ElseWhereOp : hlfir_Op<"elsewhere", [Terminator,
+    ParentOneOf<["WhereOp", "ElseWhereOp"]>, hlfir_OrderedAssignmentTreeOpInterface]> {
+  let summary = "Represent a Fortran elsewhere statement";
+
+  let description = [{
+    Represent Fortran "elsewhere" construct or statement.
+
+    It has an optional mask region to hold the evaluation of Fortran
+    optional elsewhere mask expressions. If this region is provided,
+    it must satisfy the same constraints as hlfir.where mask region.
+
+    An hlfir.elsewhere must be the last operation of an hlfir.where or,
+    hlfir.elsewhere body, which is enforced by its terminator property.
+
+    Like in Fortran, an hlfir.elsewhere negate the current control mask,
+    and if provided, adds the mask the resulting control mask (with a logical
+    AND).
+  }];
+
+  let regions = (region  MaxSizedRegion<1>:$mask_region,
+                         SizedRegion<1>:$body);
+
+  let extraClassDeclaration = [{
+    void getLeafRegions(llvm::SmallVectorImpl<mlir::Region*>& regions) {
+      if (!getMaskRegion().empty())
+        regions.push_back(&getMaskRegion());
+    }
+    mlir::Region* getSubTreeRegion() { return &getBody(); }
+  }];
+
+  let assemblyFormat = [{
+    (`mask` $mask_region^)?
+    attr-dict `do`
+    custom<AssignmentMaskOpBody>($body)
+  }];
+  let hasVerifier = 1;
+}
+
 #endif // FORTRAN_DIALECT_HLFIR_OPS
diff --git a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
index c03b7c92248fb..7220c0860fc27 100644
--- a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
+++ b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
@@ -1151,6 +1151,81 @@ static bool yieldsIntegerOrEmpty(mlir::Region &region) {
   return yield && fir::isa_integer(yield.getEntity().getType());
 }
 
+//===----------------------------------------------------------------------===//
+// ForallMaskOp
+//===----------------------------------------------------------------------===//
+
+static mlir::ParseResult parseAssignmentMaskOpBody(mlir::OpAsmParser &parser,
+                                                   mlir::Region &body) {
+  if (parser.parseRegion(body))
+    return mlir::failure();
+  ensureTerminator(body, parser.getBuilder(),
+                   parser.getBuilder().getUnknownLoc());
+  return mlir::success();
+}
+
+template <typename ConcreteOp>
+static void printAssignmentMaskOpBody(mlir::OpAsmPrinter &p, ConcreteOp,
+                                      mlir::Region &body) {
+  // ElseWhereOp is a WhereOp/ElseWhereOp terminator that should be printed.
+  bool printBlockTerminators =
+      !body.empty() &&
+      mlir::isa_and_nonnull<hlfir::ElseWhereOp>(body.back().getTerminator());
+  p.printRegion(body, /*printEntryBlockArgs=*/false, printBlockTerminators);
+}
+
+static bool yieldsLogical(mlir::Region &region, bool mustBeScalarI1) {
+  if (region.empty())
+    return false;
+  auto yield = mlir::dyn_cast_or_null<hlfir::YieldOp>(getTerminator(region));
+  if (!yield)
+    return false;
+  mlir::Type yieldType = yield.getEntity().getType();
+  if (mustBeScalarI1)
+    return hlfir::isI1Type(yieldType);
+  return hlfir::isMaskArgument(yieldType) &&
+         hlfir::getFortranElementOrSequenceType(yieldType)
+             .isa<fir::SequenceType>();
+}
+
+mlir::LogicalResult hlfir::ForallMaskOp::verify() {
+  if (!yieldsLogical(getMaskRegion(), /*mustBeScalarI1=*/true))
+    return emitOpError("mask region must yield a scalar i1");
+  mlir::Operation *op = getOperation();
+  hlfir::ForallOp forallOp =
+      mlir::dyn_cast_or_null<hlfir::ForallOp>(op->getParentOp());
+  if (!forallOp || op->getParentRegion() != &forallOp.getBody())
+    return emitOpError("must be inside the body region of an hlfir.forall");
+  return mlir::success();
+}
+
+//===----------------------------------------------------------------------===//
+// WhereOp and ElseWhereOp
+//===----------------------------------------------------------------------===//
+
+template <typename ConcreteOp>
+static mlir::LogicalResult verifyWhereAndElseWhereBody(ConcreteOp &concreteOp) {
+  for (mlir::Operation &op : concreteOp.getBody().front())
+    if (mlir::isa<hlfir::ForallOp>(op))
+      return concreteOp.emitOpError(
+          "body region must not contain hlfir.forall");
+  return mlir::success();
+}
+
+mlir::LogicalResult hlfir::WhereOp::verify() {
+  if (!yieldsLogical(getMaskRegion(), /*mustBeScalarI1=*/false))
+    return emitOpError("mask region must yield a logical array");
+  return verifyWhereAndElseWhereBody(*this);
+}
+
+mlir::LogicalResult hlfir::ElseWhereOp::verify() {
+  if (!getMaskRegion().empty())
+    if (!yieldsLogical(getMaskRegion(), /*mustBeScalarI1=*/false))
+      return emitOpError(
+          "mask region must yield a logical array when provided");
+  return verifyWhereAndElseWhereBody(*this);
+}
+
 #include "flang/Optimizer/HLFIR/HLFIROpInterfaces.cpp.inc"
 #define GET_OP_CLASSES
 #include "flang/Optimizer/HLFIR/HLFIROps.cpp.inc"
diff --git a/flang/test/HLFIR/elsewhere.fir b/flang/test/HLFIR/elsewhere.fir
new file mode 100644
index 0000000000000..b0033a6dc5b4f
--- /dev/null
+++ b/flang/test/HLFIR/elsewhere.fir
@@ -0,0 +1,82 @@
+// Test hlfir.elsewhere operation parse, verify (no errors), and unparse.
+// RUN: fir-opt %s | fir-opt | FileCheck %s
+
+func.func @test_elsewhere(%mask: !fir.ref<!fir.array<10x!fir.logical<4>>>, %x: !fir.ref<!fir.array<10xf32>>, %y: !fir.box<!fir.array<?xf32>>) {
+  hlfir.where {
+    hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+  } do {
+    hlfir.elsewhere do {
+      hlfir.region_assign {
+        hlfir.yield %y : !fir.box<!fir.array<?xf32>>
+      } to {
+        hlfir.yield %x : !fir.ref<!fir.array<10xf32>>
+      }
+    }
+  }
+  return
+}
+// CHECK-LABEL:   func.func @test_elsewhere(
+// CHECK-SAME:                              %[[VAL_0:.*]]: !fir.ref<!fir.array<10x!fir.logical<4>>>,
+// CHECK-SAME:                              %[[VAL_1:.*]]: !fir.ref<!fir.array<10xf32>>,
+// CHECK-SAME:                              %[[VAL_2:.*]]: !fir.box<!fir.array<?xf32>>) {
+// CHECK:           hlfir.where {
+// CHECK:             hlfir.yield %[[VAL_0]] : !fir.ref<!fir.array<10x!fir.logical<4>>>
+// CHECK:           } do {
+// CHECK:             hlfir.elsewhere do {
+// CHECK:               hlfir.region_assign {
+// CHECK:                 hlfir.yield %[[VAL_2]] : !fir.box<!fir.array<?xf32>>
+// CHECK:               } to {
+// CHECK:                 hlfir.yield %[[VAL_1]] : !fir.ref<!fir.array<10xf32>>
+// CHECK:               }
+// CHECK:             }
+// CHECK:           }
+
+func.func @test_masked_elsewhere(%mask: !fir.ref<!fir.array<10x!fir.logical<4>>>, %x: !fir.ref<!fir.array<10xf32>>, %y: !fir.box<!fir.array<?xf32>>) {
+  hlfir.where {
+    hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+  } do {
+    hlfir.elsewhere mask {
+      %other_mask = fir.call @get_mask() : () -> !fir.ptr<!fir.array<10x!fir.logical<4>>>
+      hlfir.yield %other_mask : !fir.ptr<!fir.array<10x!fir.logical<4>>>
+    } do {
+      hlfir.region_assign {
+        hlfir.yield %y : !fir.box<!fir.array<?xf32>>
+      } to {
+        hlfir.yield %x : !fir.ref<!fir.array<10xf32>>
+      }
+      hlfir.elsewhere do {
+        hlfir.region_assign {
+          hlfir.yield %x : !fir.ref<!fir.array<10xf32>>
+        } to {
+          hlfir.yield %y : !fir.box<!fir.array<?xf32>>
+        }
+      }
+    }
+  }
+  return
+}
+// CHECK-LABEL:   func.func @test_masked_elsewhere(
+// CHECK-SAME:                                     %[[VAL_0:.*]]: !fir.ref<!fir.array<10x!fir.logical<4>>>,
+// CHECK-SAME:                                     %[[VAL_1:.*]]: !fir.ref<!fir.array<10xf32>>,
+// CHECK-SAME:                                     %[[VAL_2:.*]]: !fir.box<!fir.array<?xf32>>) {
+// CHECK:           hlfir.where {
+// CHECK:             hlfir.yield %[[VAL_0]] : !fir.ref<!fir.array<10x!fir.logical<4>>>
+// CHECK:           } do {
+// CHECK:             hlfir.elsewhere mask {
+// CHECK:               %[[VAL_3:.*]] = fir.call @get_mask() : () -> !fir.ptr<!fir.array<10x!fir.logical<4>>>
+// CHECK:               hlfir.yield %[[VAL_3]] : !fir.ptr<!fir.array<10x!fir.logical<4>>>
+// CHECK:             } do {
+// CHECK:               hlfir.region_assign {
+// CHECK:                 hlfir.yield %[[VAL_2]] : !fir.box<!fir.array<?xf32>>
+// CHECK:               } to {
+// CHECK:                 hlfir.yield %[[VAL_1]] : !fir.ref<!fir.array<10xf32>>
+// CHECK:               }
+// CHECK:               hlfir.elsewhere do {
+// CHECK:                 hlfir.region_assign {
+// CHECK:                   hlfir.yield %[[VAL_1]] : !fir.ref<!fir.array<10xf32>>
+// CHECK:                 } to {
+// CHECK:                   hlfir.yield %[[VAL_2]] : !fir.box<!fir.array<?xf32>>
+// CHECK:                 }
+// CHECK:               }
+// CHECK:             }
+// CHECK:           }
diff --git a/flang/test/HLFIR/forall_mask.fir b/flang/test/HLFIR/forall_mask.fir
new file mode 100644
index 0000000000000..b0ca270084e38
--- /dev/null
+++ b/flang/test/HLFIR/forall_mask.fir
@@ -0,0 +1,49 @@
+// Test hlfir.forall_mask operation parse, verify (no errors), and unparse.
+// RUN: fir-opt %s | fir-opt | FileCheck %s
+
+func.func @forall_mask_test(%x: !fir.box<!fir.array<?xf32>>) {
+  %c1 = arith.constant 1 : index
+  %c10 = arith.constant 10 : index
+  hlfir.forall lb {
+    hlfir.yield %c1 : index
+  } ub {
+    hlfir.yield %c10 : index
+  } (%i : index) {
+    hlfir.forall_mask {
+      %mask = fir.call @some_condition(%i) : (index) -> i1
+      hlfir.yield %mask : i1
+    } do {
+      hlfir.region_assign {
+        %res = fir.call @foo(%i) : (index) -> f32
+        hlfir.yield %res : f32
+      } to {
+        %xi = hlfir.designate %x(%i) : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+        hlfir.yield %xi : !fir.ref<f32>
+      }
+    }
+  }
+  return
+}
+
+// CHECK-LABEL:   func.func @forall_mask_test(
+// CHECK-SAME:                                %[[VAL_0:.*]]: !fir.box<!fir.array<?xf32>>) {
+// CHECK:           %[[VAL_1:.*]] = arith.constant 1 : index
+// CHECK:           %[[VAL_2:.*]] = arith.constant 10 : index
+// CHECK:           hlfir.forall lb {
+// CHECK:             hlfir.yield %[[VAL_1]] : index
+// CHECK:           } ub {
+// CHECK:             hlfir.yield %[[VAL_2]] : index
+// CHECK:           }  (%[[VAL_3:.*]]: index) {
+// CHECK:             hlfir.forall_mask {
+// CHECK:               %[[VAL_4:.*]] = fir.call @some_condition(%[[VAL_3]]) : (index) -> i1
+// CHECK:               hlfir.yield %[[VAL_4]] : i1
+// CHECK:             } do {
+// CHECK:               hlfir.region_assign {
+// CHECK:                 %[[VAL_5:.*]] = fir.call @foo(%[[VAL_3]]) : (index) -> f32
+// CHECK:                 hlfir.yield %[[VAL_5]] : f32
+// CHECK:               } to {
+// CHECK:                 %[[VAL_6:.*]] = hlfir.designate %[[VAL_0]] (%[[VAL_3]])  : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+// CHECK:                 hlfir.yield %[[VAL_6]] : !fir.ref<f32>
+// CHECK:               }
+// CHECK:             }
+// CHECK:           }
diff --git a/flang/test/HLFIR/invalid.fir b/flang/test/HLFIR/invalid.fir
index c1bcdaf687c78..29b61f0487c21 100644
--- a/flang/test/HLFIR/invalid.fir
+++ b/flang/test/HLFIR/invalid.fir
@@ -642,3 +642,110 @@ func.func @bad_forall_2(%x : !fir.box<!fir.array<10xf32>>, %y: f32) {
   }
   return
 }
+
+// -----
+func.func @bad_forall_mask(%i: index) {
+  // expected-error@+1 {{'hlfir.forall_mask' op must be inside the body region of an hlfir.forall}}
+  hlfir.forall_mask {
+    %mask = fir.call @some_condition(%i) : (index) -> i1
+    hlfir.yield %mask : i1
+  } do {
+  }
+  return
+}
+
+// -----
+func.func @bad_forall_mask_2(%mask: !fir.ref<!fir.array<10x!fir.logical<4>>>) {
+  %c1 = arith.constant 1 : index
+  hlfir.forall lb {
+    hlfir.yield %c1 : index
+  } ub {
+    hlfir.yield %c1 : index
+  } (%i: index) {
+    // expected-error@+1 {{'hlfir.forall_mask' op mask region must yield a scalar i1}}
+    hlfir.forall_mask {
+      hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+    } do {
+    }
+  }
+  return
+}
+
+// -----
+func.func @bad_where_1(%bad_mask: !fir.ref<!fir.array<10xf32>>) {
+  // expected-error@+1 {{'hlfir.where' op mask region must yield a logical array}}
+  hlfir.where {
+    hlfir.yield %bad_mask : !fir.ref<!fir.array<10xf32>>
+  } do {
+  }
+  return
+}
+
+// -----
+func.func @bad_where_2(%bad_mask: i1) {
+  // expected-error@+1 {{'hlfir.where' op mask region must yield a logical array}}
+  hlfir.where {
+    hlfir.yield %bad_mask : i1
+  } do {
+  }
+  return
+}
+
+// -----
+func.func @bad_where_3(%mask: !fir.ref<!fir.array<10x!fir.logical<4>>>, %n: index) {
+  // expected-error@+1 {{'hlfir.where' op body region must not contain hlfir.forall}}
+  hlfir.where {
+    hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+  } do {
+    hlfir.forall lb {
+      hlfir.yield %n : index
+    } ub {
+      hlfir.yield %n : index
+    } (%i: index) {
+    }
+  }
+  return
+}
+
+// -----
+func.func @bad_elsewhere_1(%mask: !fir.ref<!fir.array<10x!fir.logical<4>>>, %bad_mask: i1) {
+  hlfir.where {
+    hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+  } do {
+    // expected-error@+1 {{'hlfir.elsewhere' op mask region must yield a logical array when provided}}
+    hlfir.elsewhere mask {
+      hlfir.yield %bad_mask : i1
+    } do {
+    }
+  }
+  return
+}
+
+// -----
+func.func @bad_elsewhere_2(%mask: !fir.ref<!fir.array<10x!fir.logical<4>>>) {
+  // expected-error@+1 {{'hlfir.elsewhere' op expects parent op to be one of 'hlfir.where, hlfir.elsewhere'}}
+  hlfir.elsewhere mask {
+    hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+  } do {
+  }
+  return
+}
+
+// -----
+func.func @bad_elsewhere_3(%mask: !fir.ref<!fir.array<10x!fir.logical<4>>>, %x: !fir.ref<!fir.array<10xf32>>, %y: !fir.box<!fir.array<?xf32>>) {
+  hlfir.where {
+    hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+  } do {
+    // expected-error@+1 {{'hlfir.elsewhere' op must be the last operation in the parent block}}
+    hlfir.elsewhere mask {
+      hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+    } do {
+    }
+    hlfir.region_assign {
+      hlfir.yield %y : !fir.box<!fir.array<?xf32>>
+    } to {
+      hlfir.yield %x : !fir.ref<!fir.array<10xf32>>
+    }
+  }
+  return
+}
diff --git a/flang/test/HLFIR/where.fir b/flang/test/HLFIR/where.fir
new file mode 100644
index 0000000000000..2aa242c9491df
--- /dev/null
+++ b/flang/test/HLFIR/where.fir
@@ -0,0 +1,28 @@
+// Test hlfir.where operation parse, verify (no errors), and unparse.
+// RUN: fir-opt %s | fir-opt | FileCheck %s
+
+func.func @test_where(%mask: !fir.ref<!fir.array<10x!fir.logical<4>>>, %x: !fir.ref<!fir.array<10xf32>>, %y: !fir.box<!fir.array<?xf32>>) {
+  hlfir.where {
+    hlfir.yield %mask : !fir.ref<!fir.array<10x!fir.logical<4>>>
+  } do {
+    hlfir.region_assign {
+      hlfir.yield %y : !fir.box<!fir.array<?xf32>>
+    } to {
+      hlfir.yield %x : !fir.ref<!fir.array<10xf32>>
+    }
+  }
+  return
+}
+// CHECK-LABEL:   func.func @test_where(
+// CHECK-SAME:                          %[[VAL_0:.*]]: !fir.ref<!fir.array<10x!fir.logical<4>>>,
+// CHECK-SAME:                          %[[VAL_1:.*]]: !fir.ref<!fir.array<10xf32>>,
+// CHECK-SAME:                          %[[VAL_2:.*]]: !fir.box<!fir.array<?xf32>>) {
+// CHECK:           hlfir.where {
+// CHECK:             hlfir.yield %[[VAL_0]] : !fir.ref<!fir.array<10x!fir.logical<4>>>
+// CHECK:           } do {
+// CHECK:             hlfir.region_assign {
+// CHECK:               hlfir.yield %[[VAL_2]] : !fir.box<!fir.array<?xf32>>
+// CHECK:             } to {
+// CHECK:               hlfir.yield %[[VAL_1]] : !fir.ref<!fir.array<10xf32>>
+// CHECK:             }
+// CHECK:           }