diff --git a/include/mlir-hlo/Dialect/mhlo/IR/chlo_ops.td b/include/mlir-hlo/Dialect/mhlo/IR/chlo_ops.td
index 92ae4d2..13d5f02 100644
--- a/include/mlir-hlo/Dialect/mhlo/IR/chlo_ops.td
+++ b/include/mlir-hlo/Dialect/mhlo/IR/chlo_ops.td
@@ -360,6 +360,19 @@ def HLOClient_AcosOp : HLOClient_UnaryElementwiseOp<"acos", [],
   }];
 }
 
+def HLOClient_AtanOp : HLOClient_UnaryElementwiseOp<"atan", [],
+    HLO_FpOrComplexTensor> {
+  let summary = "Atan operator";
+
+  let description = [{
+    Returns `Atan(operand)` element-wise.
+
+    $$
+    \atan(x) = \atan2(x, 1)
+    $$
+  }];
+}
+
 def HLOClient_SinhOp : HLOClient_UnaryElementwiseOp<"sinh", [],
     HLO_FpOrComplexTensor> {
   let summary = "Sinh operation";
diff --git a/include/mlir-hlo/Dialect/mhlo/transforms/map_lmhlo_to_scalar_op.h b/include/mlir-hlo/Dialect/mhlo/transforms/map_lmhlo_to_scalar_op.h
index d2fb048..9cf1b6c 100644
--- a/include/mlir-hlo/Dialect/mhlo/transforms/map_lmhlo_to_scalar_op.h
+++ b/include/mlir-hlo/Dialect/mhlo/transforms/map_lmhlo_to_scalar_op.h
@@ -149,6 +149,15 @@ inline Value MapLhloOpToStdScalarOp<lmhlo::AndOp>(Location loc,
       loc, result_types, args, b);
 }
 
+template <>
+inline Value MapLhloOpToStdScalarOp<lmhlo::Atan2Op>(Location loc,
+                                                    ArrayRef<Type> result_types,
+                                                    ArrayRef<Value> args,
+                                                    OpBuilder* b) {
+  return MapLhloOpToStdScalarOpImpl<FloatType, ::mlir::Atan2Op>{}(
+      loc, result_types, args, b);
+}
+
 template <typename PredicateType>
 inline Optional<PredicateType> getCmpPredicate(StringRef comparison_direction) {
   return llvm::None;
diff --git a/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td b/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td
index 9d9e6d9..fb4bf3a 100644
--- a/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td
+++ b/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td
@@ -49,6 +49,14 @@ def : Pat<(HLOClient_AcosOp $input),
     ),
     (HLO_ConstantLike<"M_PI"> $input))>;
 
+// Express `atan` as
+//   atan(x) = atan2(x, 1)
+def : Pat<(HLOClient_AtanOp $input),
+  (HLO_Atan2Op
+    $input,
+    (HLO_ConstantLike<"1"> $input)
+  )>;
+
 // Express `sinh` as
 //   sinh(x) = (e^x - e^-x) / 2                     if |x| < 1
 //           = e^(x + log(1/2)) - e^(-x + log(1/2)) otherwise.
@@ -95,4 +103,3 @@ def : Pat<(HLOClient_TanOp $input),
     (HLO_SinOp $input),
     (HLO_CosOp $input)
   )>;
-
diff --git a/lib/Dialect/mhlo/transforms/legalize_to_linalg.cc b/lib/Dialect/mhlo/transforms/legalize_to_linalg.cc
index 2d36b1c..57859b6 100644
--- a/lib/Dialect/mhlo/transforms/legalize_to_linalg.cc
+++ b/lib/Dialect/mhlo/transforms/legalize_to_linalg.cc
@@ -822,6 +822,7 @@ void populateLHLOToLinalgConversionPattern(MLIRContext* context,
                    PointwiseToLinalgConverter<lmhlo::AbsOp>,
                    PointwiseToLinalgConverter<lmhlo::AddOp>,
                    PointwiseToLinalgConverter<lmhlo::AndOp>,
+                   PointwiseToLinalgConverter<lmhlo::Atan2Op>,
                    PointwiseToLinalgConverter<lmhlo::CeilOp>,
                    PointwiseToLinalgConverter<lmhlo::CompareOp>,
                    PointwiseToLinalgConverter<lmhlo::ComplexOp>,
@@ -932,6 +933,7 @@ void populateHLOToLinalgConversionPattern(MLIRContext* context,
                PointwiseToLinalgConverter<mhlo::AbsOp, false>,
                PointwiseToLinalgConverter<mhlo::AddOp, false>,
                PointwiseToLinalgConverter<mhlo::AndOp, false>,
+               PointwiseToLinalgConverter<mhlo::Atan2Op, false>,
                PointwiseToLinalgConverter<mhlo::CeilOp, false>,
                PointwiseToLinalgConverter<mhlo::CompareOp, false>,
                PointwiseToLinalgConverter<mhlo::ComplexOp, false>,
diff --git a/lib/Dialect/mhlo/transforms/transform_unranked_hlo.cc b/lib/Dialect/mhlo/transforms/transform_unranked_hlo.cc
index 0be4c68..7c01fa2 100644
--- a/lib/Dialect/mhlo/transforms/transform_unranked_hlo.cc
+++ b/lib/Dialect/mhlo/transforms/transform_unranked_hlo.cc
@@ -48,7 +48,7 @@ namespace {
 
 // TODO(herhut): Generate these out of op definitions.
 #define MAP_CHLO_OPERATION_CWISE_UNARY(fn, sep) \
-  fn(TanOp) sep fn(AcosOp) sep fn(SinhOp)
+  fn(AcosOp) sep fn(AtanOp) sep fn(SinhOp) sep fn(TanOp)
 
 template <typename OpTy>
 inline void AddLegalOpOnRankedTensor(ConversionTarget *target) {