diff --git a/flang/include/flang/Semantics/symbol.h b/flang/include/flang/Semantics/symbol.h
--- a/flang/include/flang/Semantics/symbol.h
+++ b/flang/include/flang/Semantics/symbol.h
@@ -14,6 +14,8 @@
 #include "flang/Common/enum-set.h"
 #include "flang/Common/reference.h"
 #include "flang/Common/visit.h"
+#include "flang/Parser/parse-tree.h"
+#include "llvm/ADT/BitmaskEnum.h"
 #include "llvm/ADT/DenseMapInfo.h"
 
 #include <array>
@@ -45,8 +47,47 @@
 using MutableSymbolRef = common::Reference<Symbol>;
 using MutableSymbolVector = std::vector<MutableSymbolRef>;
 
+namespace {
+LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE();
+// Flags representing OpenMP requires clauses.
+enum OmpRequiresFlags {
+  None = 0x00,
+  ReverseOffload = 0x01,
+  UnifiedAddress = 0x02,
+  UnifiedSharedMemory = 0x04,
+  DynamicAllocators = 0x08,
+  LLVM_MARK_AS_BITMASK_ENUM(DynamicAllocators)
+};
+} // namespace
+
+// Mixin for details with OpenMP declarative constructs.
+class WithOmpDeclarative {
+  using OmpAtomicOrderType = parser::OmpAtomicDefaultMemOrderClause::Type;
+
+public:
+  bool has_ompRequires() const { return ompRequires_.has_value(); }
+  const OmpRequiresFlags *ompRequires() const {
+    return ompRequires_ ? &*ompRequires_ : nullptr;
+  }
+  void set_ompRequires(OmpRequiresFlags flags) { ompRequires_ = flags; }
+
+  bool has_ompAtomicDefaultMemOrder() const {
+    return ompAtomicDefaultMemOrder_.has_value();
+  }
+  const OmpAtomicOrderType *ompAtomicDefaultMemOrder() const {
+    return ompAtomicDefaultMemOrder_ ? &*ompAtomicDefaultMemOrder_ : nullptr;
+  }
+  void set_ompAtomicDefaultMemOrder(OmpAtomicOrderType flags) {
+    ompAtomicDefaultMemOrder_ = flags;
+  }
+
+private:
+  std::optional<OmpRequiresFlags> ompRequires_;
+  std::optional<OmpAtomicOrderType> ompAtomicDefaultMemOrder_;
+};
+
 // A module or submodule.
-class ModuleDetails {
+class ModuleDetails : public WithOmpDeclarative {
 public:
   ModuleDetails(bool isSubmodule = false) : isSubmodule_{isSubmodule} {}
   bool isSubmodule() const { return isSubmodule_; }
@@ -63,7 +104,7 @@
   const Scope *scope_{nullptr};
 };
 
-class MainProgramDetails {
+class MainProgramDetails : public WithOmpDeclarative {
 public:
 private:
 };
@@ -85,7 +126,7 @@
 // A subroutine or function definition, or a subprogram interface defined
 // in an INTERFACE block as part of the definition of a dummy procedure
 // or a procedure pointer (with just POINTER).
-class SubprogramDetails : public WithBindName {
+class SubprogramDetails : public WithBindName, public WithOmpDeclarative {
 public:
   bool isFunction() const { return result_ != nullptr; }
   bool isInterface() const { return isInterface_; }
diff --git a/flang/lib/Parser/openmp-parsers.cpp b/flang/lib/Parser/openmp-parsers.cpp
--- a/flang/lib/Parser/openmp-parsers.cpp
+++ b/flang/lib/Parser/openmp-parsers.cpp
@@ -608,7 +608,7 @@
 
 // 2.4 Requires construct
 TYPE_PARSER(sourced(construct<OpenMPRequiresConstruct>(
-    verbatim("REQUIRES"_tok), some(Parser<OmpClause>{} / maybe(","_tok)))))
+    verbatim("REQUIRES"_tok), Parser<OmpClauseList>{})))
 
 // 2.15.2 Threadprivate directive
 TYPE_PARSER(sourced(construct<OpenMPThreadprivate>(
diff --git a/flang/lib/Semantics/canonicalize-omp.cpp b/flang/lib/Semantics/canonicalize-omp.cpp
--- a/flang/lib/Semantics/canonicalize-omp.cpp
+++ b/flang/lib/Semantics/canonicalize-omp.cpp
@@ -17,7 +17,10 @@
 //      after this pass.
 //   2. Associate declarative OMP allocation directives with their
 //      respective executable allocation directive
-//   3. TBD
+//   3. set the default memory order, defined by any 'requires' directive
+//      present in the compilation unit, as explicit memory order of all atomic
+//      operations that don't already have it specified.
+//   4. TBD
 namespace Fortran::semantics {
 
 using namespace parser::literals;
@@ -50,6 +53,26 @@
 
   void Post(parser::ExecutionPart &body) { RewriteOmpAllocations(body); }
 
+  // Assume at this point that any such clauses appear only on 'requires'
+  // directives that are visited before any atomic operations, and that all
+  // instances (if present) specify the same ordering. Other semantic checks
+  // later ensure that these restrictions are met.
+  void Post(parser::OmpClause::AtomicDefaultMemOrder &x) {
+    switch (x.v.v) {
+    case parser::OmpAtomicDefaultMemOrderClause::Type::AcqRel:
+      atomicDefaultMemOrder_ = llvm::omp::Clause::OMPC_acq_rel;
+      break;
+    case parser::OmpAtomicDefaultMemOrderClause::Type::Relaxed:
+      atomicDefaultMemOrder_ = llvm::omp::Clause::OMPC_relaxed;
+      break;
+    case parser::OmpAtomicDefaultMemOrderClause::Type::SeqCst:
+      atomicDefaultMemOrder_ = llvm::omp::Clause::OMPC_seq_cst;
+      break;
+    }
+  }
+
+  void Post(parser::OpenMPAtomicConstruct &atomic) { RewriteOmpAtomic(atomic); }
+
 private:
   template <typename T> T *GetConstructIf(parser::ExecutionPartConstruct &x) {
     if (auto *y{std::get_if<parser::ExecutableConstruct>(&x.u)}) {
@@ -149,7 +172,68 @@
     }
   }
 
+  void RewriteOmpAtomic(parser::OpenMPAtomicConstruct &atomic) {
+    // Rewrite atomic constructs to add an explicit memory ordering to all
+    // that do not specify it, honoring in this way the
+    // `atomic_default_mem_order` clause of the 'requires' directive.
+    if (!atomicDefaultMemOrder_) {
+      return;
+    }
+
+    auto findMemOrderClause =
+        [](const std::list<parser::OmpAtomicClause> &clauses) {
+          return std::find_if(
+                     clauses.begin(), clauses.end(), [](const auto &clause) {
+                       return std::get_if<parser::OmpMemoryOrderClause>(
+                           &clause.u);
+                     }) != clauses.end();
+        };
+
+    // Get the clause list to which the new memory order clause must be added,
+    // only if there are no other memory order clauses present for this atomic
+    // directive.
+    auto *clauseList = common::visit(
+        common::visitors{[&](parser::OmpAtomic &atomicConstruct) {
+                           // OmpAtomic only has a single list of clauses.
+                           auto &clauses{std::get<parser::OmpAtomicClauseList>(
+                               atomicConstruct.t)};
+                           return !findMemOrderClause(clauses.v) ? &clauses.v
+                                                                 : nullptr;
+                         },
+            [&](auto &atomicConstruct) {
+              // All other atomic constructs have two lists of clauses.
+              auto &clausesLhs{std::get<0>(atomicConstruct.t)};
+              auto &clausesRhs{std::get<2>(atomicConstruct.t)};
+              return !findMemOrderClause(clausesLhs.v) &&
+                      !findMemOrderClause(clausesRhs.v)
+                  ? &clausesRhs.v
+                  : nullptr;
+            }},
+        atomic.u);
+
+    if (clauseList) {
+      switch (*atomicDefaultMemOrder_) {
+      case llvm::omp::Clause::OMPC_acq_rel:
+        clauseList->push_back(parser::OmpMemoryOrderClause(
+            parser::OmpClause(parser::OmpClause::AcqRel())));
+        break;
+      case llvm::omp::Clause::OMPC_relaxed:
+        clauseList->push_back(parser::OmpMemoryOrderClause(
+            parser::OmpClause(parser::OmpClause::Relaxed())));
+        break;
+      case llvm::omp::Clause::OMPC_seq_cst:
+        clauseList->push_back(parser::OmpMemoryOrderClause(
+            parser::OmpClause(parser::OmpClause::SeqCst())));
+        break;
+      default:
+        llvm_unreachable("Unexpected clause used as memory ordering");
+        break;
+      }
+    }
+  }
+
   parser::Messages &messages_;
+  std::optional<llvm::omp::Clause> atomicDefaultMemOrder_;
 };
 
 bool CanonicalizeOmp(parser::Messages &messages, parser::Program &program) {
diff --git a/flang/lib/Semantics/check-omp-structure.h b/flang/lib/Semantics/check-omp-structure.h
--- a/flang/lib/Semantics/check-omp-structure.h
+++ b/flang/lib/Semantics/check-omp-structure.h
@@ -182,6 +182,8 @@
   void Enter(const parser::OmpAtomicCapture &);
   void Leave(const parser::OmpAtomic &);
 
+  void Enter(const parser::UseStmt &);
+
 #define GEN_FLANG_CLAUSE_CHECK_ENTER
 #include "llvm/Frontend/OpenMP/OMP.inc"
 
@@ -268,6 +270,7 @@
       const parser::OmpObjectList &ompObjectList);
   void CheckPredefinedAllocatorRestriction(
       const parser::CharBlock &source, const parser::Name &name);
+  void CheckAllowedRequiresClause(llvmOmpClause clause);
   bool isPredefinedAllocator{false};
   void EnterDirectiveNest(const int index) { directiveNest_[index]++; }
   void ExitDirectiveNest(const int index) { directiveNest_[index]--; }
@@ -281,6 +284,9 @@
     LastType
   };
   int directiveNest_[LastType + 1] = {0};
+
+  bool deviceConstructFound_{false};
+  bool atomicDirectiveDefaultOrderFound_{false};
 };
 } // namespace Fortran::semantics
 #endif // FORTRAN_SEMANTICS_CHECK_OMP_STRUCTURE_H_
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -789,6 +789,7 @@
 
   switch (beginDir.v) {
   case llvm::omp::Directive::OMPD_target:
+    deviceConstructFound_ = true;
     if (CheckTargetBlockOnlyTeams(block)) {
       EnterDirectiveNest(TargetBlockOnlyTeams);
     }
@@ -1155,21 +1156,40 @@
   const auto &dir{std::get<parser::Verbatim>(x.t)};
   const auto &spec{std::get<parser::OmpDeclareTargetSpecifier>(x.t)};
   if (const auto *objectList{parser::Unwrap<parser::OmpObjectList>(spec.u)}) {
+    deviceConstructFound_ = true;
     CheckSymbolNames(dir.source, *objectList);
     CheckIsVarPartOfAnotherVar(dir.source, *objectList);
     CheckThreadprivateOrDeclareTargetVar(*objectList);
   } else if (const auto *clauseList{
                  parser::Unwrap<parser::OmpClauseList>(spec.u)}) {
+    bool toClauseFound{false}, deviceTypeClauseFound{false};
     for (const auto &clause : clauseList->v) {
-      if (const auto *toClause{std::get_if<parser::OmpClause::To>(&clause.u)}) {
-        CheckSymbolNames(dir.source, toClause->v);
-        CheckIsVarPartOfAnotherVar(dir.source, toClause->v);
-        CheckThreadprivateOrDeclareTargetVar(toClause->v);
-      } else if (const auto *linkClause{
-                     std::get_if<parser::OmpClause::Link>(&clause.u)}) {
-        CheckSymbolNames(dir.source, linkClause->v);
-        CheckIsVarPartOfAnotherVar(dir.source, linkClause->v);
-        CheckThreadprivateOrDeclareTargetVar(linkClause->v);
+      common::visit(
+          common::visitors{
+              [&](const parser::OmpClause::To &toClause) {
+                toClauseFound = true;
+                CheckSymbolNames(dir.source, toClause.v);
+                CheckIsVarPartOfAnotherVar(dir.source, toClause.v);
+                CheckThreadprivateOrDeclareTargetVar(toClause.v);
+              },
+              [&](const parser::OmpClause::Link &linkClause) {
+                CheckSymbolNames(dir.source, linkClause.v);
+                CheckIsVarPartOfAnotherVar(dir.source, linkClause.v);
+                CheckThreadprivateOrDeclareTargetVar(linkClause.v);
+              },
+              [&](const parser::OmpClause::DeviceType &deviceTypeClause) {
+                deviceTypeClauseFound = true;
+                if (deviceTypeClause.v.v !=
+                    parser::OmpDeviceTypeClause::Type::Host) {
+                  deviceConstructFound_ = true;
+                }
+              },
+              [&](const auto &) {},
+          },
+          clause.u);
+
+      if (toClauseFound && !deviceTypeClauseFound) {
+        deviceConstructFound_ = true;
       }
     }
   }
@@ -1671,6 +1691,9 @@
   if (rightHandClauseList) {
     checkForValidMemoryOrderClause(rightHandClauseList);
   }
+  if (numMemoryOrderClause == 0) {
+    atomicDirectiveDefaultOrderFound_ = true;
+  }
 }
 
 void OmpStructureChecker::Enter(const parser::OpenMPAtomicConstruct &x) {
@@ -1867,7 +1890,6 @@
 // Following clauses do not have a separate node in parse-tree.h.
 CHECK_SIMPLE_CLAUSE(AcqRel, OMPC_acq_rel)
 CHECK_SIMPLE_CLAUSE(Acquire, OMPC_acquire)
-CHECK_SIMPLE_CLAUSE(AtomicDefaultMemOrder, OMPC_atomic_default_mem_order)
 CHECK_SIMPLE_CLAUSE(Affinity, OMPC_affinity)
 CHECK_SIMPLE_CLAUSE(Allocate, OMPC_allocate)
 CHECK_SIMPLE_CLAUSE(Capture, OMPC_capture)
@@ -1877,7 +1899,6 @@
 CHECK_SIMPLE_CLAUSE(Detach, OMPC_detach)
 CHECK_SIMPLE_CLAUSE(DeviceType, OMPC_device_type)
 CHECK_SIMPLE_CLAUSE(DistSchedule, OMPC_dist_schedule)
-CHECK_SIMPLE_CLAUSE(DynamicAllocators, OMPC_dynamic_allocators)
 CHECK_SIMPLE_CLAUSE(Exclusive, OMPC_exclusive)
 CHECK_SIMPLE_CLAUSE(Final, OMPC_final)
 CHECK_SIMPLE_CLAUSE(Flush, OMPC_flush)
@@ -1890,7 +1911,6 @@
 CHECK_SIMPLE_CLAUSE(Nontemporal, OMPC_nontemporal)
 CHECK_SIMPLE_CLAUSE(Order, OMPC_order)
 CHECK_SIMPLE_CLAUSE(Read, OMPC_read)
-CHECK_SIMPLE_CLAUSE(ReverseOffload, OMPC_reverse_offload)
 CHECK_SIMPLE_CLAUSE(Threadprivate, OMPC_threadprivate)
 CHECK_SIMPLE_CLAUSE(Threads, OMPC_threads)
 CHECK_SIMPLE_CLAUSE(Inbranch, OMPC_inbranch)
@@ -1911,8 +1931,6 @@
 CHECK_SIMPLE_CLAUSE(Sizes, OMPC_sizes)
 CHECK_SIMPLE_CLAUSE(TaskReduction, OMPC_task_reduction)
 CHECK_SIMPLE_CLAUSE(To, OMPC_to)
-CHECK_SIMPLE_CLAUSE(UnifiedAddress, OMPC_unified_address)
-CHECK_SIMPLE_CLAUSE(UnifiedSharedMemory, OMPC_unified_shared_memory)
 CHECK_SIMPLE_CLAUSE(Uniform, OMPC_uniform)
 CHECK_SIMPLE_CLAUSE(Unknown, OMPC_unknown)
 CHECK_SIMPLE_CLAUSE(Untied, OMPC_untied)
@@ -2836,4 +2854,78 @@
       clause.u);
 }
 
+void OmpStructureChecker::Enter(
+    const parser::OmpClause::AtomicDefaultMemOrder &x) {
+  CheckAllowed(llvm::omp::Clause::OMPC_atomic_default_mem_order);
+
+  // Check that it does not appear after an atomic operation without
+  // memory_order defined
+  if (atomicDirectiveDefaultOrderFound_) {
+    context_.Say(GetContext().clauseSource,
+        "'%s' REQUIRES clause found lexically after atomic "
+        "operation with the '%s' clause not defined"_err_en_US,
+        parser::ToUpperCaseLetters(
+            getClauseName(llvmOmpClause::OMPC_atomic_default_mem_order).str()),
+        parser::ToUpperCaseLetters(
+            getClauseName(llvmOmpClause::OMPC_memory_order).str()));
+  }
+}
+
+void OmpStructureChecker::Enter(const parser::OmpClause::DynamicAllocators &x) {
+  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_dynamic_allocators);
+}
+
+void OmpStructureChecker::Enter(const parser::OmpClause::ReverseOffload &x) {
+  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_reverse_offload);
+}
+
+void OmpStructureChecker::Enter(const parser::OmpClause::UnifiedAddress &x) {
+  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_unified_address);
+}
+
+void OmpStructureChecker::Enter(
+    const parser::OmpClause::UnifiedSharedMemory &x) {
+  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_unified_shared_memory);
+}
+
+void OmpStructureChecker::CheckAllowedRequiresClause(llvmOmpClause clause) {
+  CheckAllowed(clause);
+
+  // Check that it does not appear after a device construct
+  if (deviceConstructFound_) {
+    context_.Say(GetContext().clauseSource,
+        "'%s' REQUIRES clause found lexically after device "
+        "construct"_err_en_US,
+        parser::ToUpperCaseLetters(getClauseName(clause).str()));
+  }
+}
+
+void OmpStructureChecker::Enter(const parser::UseStmt &x) {
+  semantics::Symbol *symbol{x.moduleName.symbol};
+  if (!symbol) {
+    // Cannot check used module if it wasn't resolved.
+    return;
+  }
+
+  auto &details = std::get<ModuleDetails>(symbol->details());
+  if (details.has_ompRequires() && deviceConstructFound_) {
+    context_.Say(x.moduleName.source,
+        "'%s' module containing device-related REQUIRES directive imported "
+        "lexically after device construct"_err_en_US,
+        x.moduleName.ToString());
+  }
+
+  if (details.has_ompAtomicDefaultMemOrder() &&
+      atomicDirectiveDefaultOrderFound_) {
+    context_.Say(x.moduleName.source,
+        "'%s' module containing '%s' REQUIRES clause imported lexically after "
+        "atomic operation with the '%s' clause not defined"_err_en_US,
+        x.moduleName.ToString(),
+        parser::ToUpperCaseLetters(
+            getClauseName(llvmOmpClause::OMPC_atomic_default_mem_order).str()),
+        parser::ToUpperCaseLetters(
+            getClauseName(llvmOmpClause::OMPC_memory_order).str()));
+  }
+}
+
 } // namespace Fortran::semantics
diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -57,6 +57,8 @@
 static llvm::raw_ostream &PutAttr(llvm::raw_ostream &, Attr);
 static llvm::raw_ostream &PutType(llvm::raw_ostream &, const DeclTypeSpec &);
 static llvm::raw_ostream &PutLower(llvm::raw_ostream &, std::string_view);
+static llvm::raw_ostream &PutOmpRequires(
+    llvm::raw_ostream &, const WithOmpDeclarative &);
 static std::error_code WriteFile(
     const std::string &, const std::string &, bool = true);
 static bool FileContentsMatch(
@@ -162,6 +164,7 @@
   uses_.str().clear();
   all << useExtraAttrs_.str();
   useExtraAttrs_.str().clear();
+  PutOmpRequires(all, details);
   all << decls_.str();
   decls_.str().clear();
   auto str{contains_.str()};
@@ -505,6 +508,8 @@
     }
   }
   os << '\n';
+  // print OpenMP requires
+  PutOmpRequires(os, details);
   // walk symbols, collect ones needed for interface
   const Scope &scope{
       details.entryScope() ? *details.entryScope() : DEREF(symbol.scope())};
@@ -874,6 +879,44 @@
   return os;
 }
 
+llvm::raw_ostream &PutOmpRequires(
+    llvm::raw_ostream &os, const WithOmpDeclarative &details) {
+  if (details.has_ompRequires() || details.has_ompAtomicDefaultMemOrder()) {
+    os << "!$omp requires";
+    if (auto *flags{details.ompRequires()}) {
+      if (*flags & OmpRequiresFlags::ReverseOffload) {
+        os << " reverse_offload";
+      }
+      if (*flags & OmpRequiresFlags::UnifiedAddress) {
+        os << " unified_address";
+      }
+      if (*flags & OmpRequiresFlags::UnifiedSharedMemory) {
+        os << " unified_shared_memory";
+      }
+      if (*flags & OmpRequiresFlags::DynamicAllocators) {
+        os << " dynamic_allocators";
+      }
+    }
+    if (auto *memOrder{details.ompAtomicDefaultMemOrder()}) {
+      os << " atomic_default_mem_order(";
+      switch (*memOrder) {
+      case parser::OmpAtomicDefaultMemOrderClause::Type::SeqCst:
+        os << "seq_cst";
+        break;
+      case parser::OmpAtomicDefaultMemOrderClause::Type::AcqRel:
+        os << "acq_rel";
+        break;
+      case parser::OmpAtomicDefaultMemOrderClause::Type::Relaxed:
+        os << "relaxed";
+        break;
+      }
+      os << ')';
+    }
+    os << '\n';
+  }
+  return os;
+}
+
 struct Temp {
   Temp(int fd, std::string path) : fd{fd}, path{path} {}
   Temp(Temp &&t) : fd{std::exchange(t.fd, -1)}, path{std::move(t.path)} {}
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -57,6 +57,12 @@
     dirContext_.emplace_back(source, dir, context_.FindScope(source));
   }
   void PopContext() { dirContext_.pop_back(); }
+  Symbol *GetDeclContext() {
+    CHECK(!declContext_.empty());
+    return declContext_.back();
+  }
+  void PushDeclContext(Symbol *symbol) { declContext_.push_back(symbol); }
+  void PopDeclContext() { declContext_.pop_back(); }
   void SetContextDirectiveSource(parser::CharBlock &dir) {
     GetContext().directiveSource = dir;
   }
@@ -108,6 +114,7 @@
   UnorderedSymbolSet dataSharingAttributeObjects_; // on one directive
   SemanticsContext &context_;
   std::vector<DirContext> dirContext_; // used as a stack
+  std::vector<Symbol *> declContext_; // used as a stack
 };
 
 class AccAttributeVisitor : DirectiveAttributeVisitor<llvm::acc::Directive> {
@@ -274,11 +281,6 @@
     return true;
   }
 
-  bool Pre(const parser::SpecificationPart &x) {
-    Walk(std::get<std::list<parser::OpenMPDeclarativeConstruct>>(x.t));
-    return true;
-  }
-
   bool Pre(const parser::StmtFunctionStmt &x) {
     const auto &parsedExpr{std::get<parser::Scalar<parser::Expr>>(x.t)};
     if (const auto *expr{GetExpr(context_, parsedExpr)}) {
@@ -326,6 +328,39 @@
 
   bool Pre(const parser::OpenMPRequiresConstruct &x) {
     PushContext(x.source, llvm::omp::Directive::OMPD_requires);
+
+    // Gather information from the clauses.
+    OmpRequiresFlags flags{OmpRequiresFlags::None};
+    std::optional<parser::OmpAtomicDefaultMemOrderClause::Type> memOrder;
+    for (auto &clause : std::get<parser::OmpClauseList>(x.t).v) {
+      flags |= common::visit(
+          common::visitors{
+              [&memOrder](
+                  const parser::OmpClause::AtomicDefaultMemOrder &atomic) {
+                memOrder = atomic.v.v;
+                return OmpRequiresFlags::None;
+              },
+              [](const parser::OmpClause::ReverseOffload &) {
+                return OmpRequiresFlags::ReverseOffload;
+              },
+              [](const parser::OmpClause::UnifiedAddress &) {
+                return OmpRequiresFlags::UnifiedAddress;
+              },
+              [](const parser::OmpClause::UnifiedSharedMemory &) {
+                return OmpRequiresFlags::UnifiedSharedMemory;
+              },
+              [](const parser::OmpClause::DynamicAllocators &) {
+                return OmpRequiresFlags::DynamicAllocators;
+              },
+              [&](const auto &) {
+                context_.Say(x.source,
+                    "Unexpected clause in REQUIRES construct"_err_en_US);
+                return OmpRequiresFlags::None;
+              }},
+          clause.u);
+    }
+    // Merge clauses into parents' symbols details.
+    AddOmpRequiresToSymbol(currScope().symbol(), flags, memOrder);
     return true;
   }
   void Post(const parser::OpenMPRequiresConstruct &) { PopContext(); }
@@ -333,6 +368,33 @@
   bool Pre(const parser::OpenMPDeclareTargetConstruct &);
   void Post(const parser::OpenMPDeclareTargetConstruct &) { PopContext(); }
 
+  void Post(const parser::UseStmt &x) {
+    Symbol *symbol{x.moduleName.symbol};
+    if (!symbol) {
+      return;
+    }
+
+    // Gather information from the imported module's symbol details.
+    OmpRequiresFlags flags{OmpRequiresFlags::None};
+    std::optional<parser::OmpAtomicDefaultMemOrderClause::Type> memOrder;
+    common::visit(
+        [&](auto &details) {
+          if constexpr (std::is_base_of_v<ModuleDetails,
+                            std::decay_t<decltype(details)>>) {
+            if (details.has_ompRequires()) {
+              flags = *details.ompRequires();
+            }
+            if (details.has_ompAtomicDefaultMemOrder()) {
+              memOrder = *details.ompAtomicDefaultMemOrder();
+            }
+          }
+        },
+        symbol->details());
+
+    // Merge requires clauses into `use` statement parents.
+    AddOmpRequiresToSymbol(GetDeclContext(), flags, memOrder);
+  }
+
   bool Pre(const parser::OpenMPThreadprivate &);
   void Post(const parser::OpenMPThreadprivate &) { PopContext(); }
 
@@ -451,6 +513,70 @@
 
   void Post(const parser::Name &);
 
+  // Keep track of contexts inside of which `SpecificationPart`s can be found
+  // to allow matching `Use` statements with their parent scopes.
+  bool Pre(const parser::MainProgram &x) {
+    const auto &end{std::get<parser::Statement<parser::EndProgramStmt>>(x.t)};
+    PushDeclContext(context_.FindScope(end.source).symbol());
+    return true;
+  }
+  bool Pre(const parser::Module &x) {
+    const auto &name{std::get<parser::Statement<parser::ModuleStmt>>(x.t)};
+    PushDeclContext(name.statement.v.symbol);
+    return true;
+  }
+  bool Pre(const parser::Submodule &x) {
+    const auto &name{std::get<parser::Statement<parser::SubmoduleStmt>>(x.t)};
+    PushDeclContext(std::get<parser::Name>(name.statement.t).symbol);
+    return true;
+  }
+  bool Pre(const parser::FunctionSubprogram &x) {
+    const auto &name{std::get<parser::Statement<parser::FunctionStmt>>(x.t)};
+    PushDeclContext(std::get<parser::Name>(name.statement.t).symbol);
+    return true;
+  }
+  bool Pre(const parser::InterfaceBody::Function &x) {
+    const auto &name{std::get<parser::Statement<parser::FunctionStmt>>(x.t)};
+    PushDeclContext(std::get<parser::Name>(name.statement.t).symbol);
+    return true;
+  }
+  bool Pre(const parser::SubroutineSubprogram &x) {
+    const auto &name{std::get<parser::Statement<parser::SubroutineStmt>>(x.t)};
+    PushDeclContext(std::get<parser::Name>(name.statement.t).symbol);
+    return true;
+  }
+  bool Pre(const parser::InterfaceBody::Subroutine &x) {
+    const auto &name{std::get<parser::Statement<parser::SubroutineStmt>>(x.t)};
+    PushDeclContext(std::get<parser::Name>(name.statement.t).symbol);
+    return true;
+  }
+  bool Pre(const parser::SeparateModuleSubprogram &x) {
+    const auto &name{
+        std::get<parser::Statement<parser::MpSubprogramStmt>>(x.t)};
+    PushDeclContext(name.statement.v.symbol);
+    return true;
+  }
+  bool Pre(const parser::BlockConstruct &x) {
+    const auto &end{std::get<parser::Statement<parser::EndBlockStmt>>(x.t)};
+    PushDeclContext(context_.FindScope(end.source).symbol());
+    return true;
+  }
+  bool Pre(const parser::BlockData &x) {
+    const auto &end{std::get<parser::Statement<parser::EndBlockDataStmt>>(x.t)};
+    PushDeclContext(context_.FindScope(end.source).symbol());
+    return true;
+  }
+  void Post(const parser::MainProgram &) { PopDeclContext(); }
+  void Post(const parser::Module &) { PopDeclContext(); }
+  void Post(const parser::Submodule &) { PopDeclContext(); }
+  void Post(const parser::FunctionSubprogram &) { PopDeclContext(); }
+  void Post(const parser::InterfaceBody::Function &) { PopDeclContext(); }
+  void Post(const parser::SubroutineSubprogram &) { PopDeclContext(); }
+  void Post(const parser::InterfaceBody::Subroutine &) { PopDeclContext(); }
+  void Post(const parser::SeparateModuleSubprogram &) { PopDeclContext(); }
+  void Post(const parser::BlockConstruct &) { PopDeclContext(); }
+  void Post(const parser::BlockData &) { PopDeclContext(); }
+
   // Keep track of labels in the statements that causes jumps to target labels
   void Post(const parser::GotoStmt &gotoStmt) { CheckSourceLabel(gotoStmt.v); }
   void Post(const parser::ComputedGotoStmt &computedGotoStmt) {
@@ -586,6 +712,9 @@
 
   bool HasSymbolInEnclosingScope(const Symbol &, Scope &);
   std::int64_t ordCollapseLevel{0};
+
+  void AddOmpRequiresToSymbol(Symbol *symbol, OmpRequiresFlags flags,
+      std::optional<parser::OmpAtomicDefaultMemOrderClause::Type> memOrder);
 };
 
 template <typename T>
@@ -1985,4 +2114,39 @@
   return llvm::is_contained(symbols, symbol);
 }
 
+void OmpAttributeVisitor::AddOmpRequiresToSymbol(Symbol *symbol,
+    OmpRequiresFlags flags,
+    std::optional<parser::OmpAtomicDefaultMemOrderClause::Type> memOrder) {
+  while (symbol) {
+    common::visit(
+        [&](auto &details) {
+          // Store clauses information into the symbol for the parent and
+          // enclosing modules, programs, functions and subroutines.
+          if constexpr (std::is_convertible_v<decltype(&details),
+                            WithOmpDeclarative *>) {
+            if (flags != OmpRequiresFlags::None) {
+              if (const OmpRequiresFlags * otherFlags{details.ompRequires()}) {
+                flags |= *otherFlags;
+              }
+              details.set_ompRequires(flags);
+            }
+            if (memOrder) {
+              if (details.has_ompAtomicDefaultMemOrder() &&
+                  *details.ompAtomicDefaultMemOrder() != *memOrder) {
+                context_.Say(symbol->scope()->sourceRange(),
+                    "Conflicting '%s' REQUIRES clauses found in compilation "
+                    "unit"_err_en_US,
+                    parser::ToUpperCaseLetters(llvm::omp::getOpenMPClauseName(
+                        llvm::omp::Clause::OMPC_atomic_default_mem_order)
+                                                   .str()));
+              }
+              details.set_ompAtomicDefaultMemOrder(*memOrder);
+            }
+          }
+        },
+        symbol->details());
+    symbol = symbol->scope()->parent().symbol();
+  }
+}
+
 } // namespace Fortran::semantics
diff --git a/flang/test/Semantics/Inputs/requires_module.f90 b/flang/test/Semantics/Inputs/requires_module.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/Inputs/requires_module.f90
@@ -0,0 +1,3 @@
+module requires_module
+  !$omp requires atomic_default_mem_order(seq_cst)
+end module
diff --git a/flang/test/Semantics/OpenMP/requires-rewrite.f90 b/flang/test/Semantics/OpenMP/requires-rewrite.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/requires-rewrite.f90
@@ -0,0 +1,76 @@
+! RUN: %flang_fc1 -fopenmp -fdebug-dump-parse-tree %s 2>&1 | FileCheck %s
+! Ensure that requires atomic_default_mem_order is used to update atomic
+! operations with no explicit memory order set.
+program requires
+  !$omp requires atomic_default_mem_order(seq_cst)
+  implicit none
+  integer :: i, j, k
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomic
+  ! CHECK-NOT: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> Relaxed
+  !$omp atomic relaxed
+  i = j
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomic
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  !$omp atomic
+  i = j
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicUpdate
+  ! CHECK-NOT: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> Relaxed
+  !$omp atomic relaxed update
+  i = j
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicUpdate
+  ! CHECK-NOT: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> Relaxed
+  !$omp atomic update relaxed
+  i = j
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicUpdate
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  !$omp atomic update
+  i = j
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicCapture
+  ! CHECK-NOT: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> Relaxed
+  !$omp atomic relaxed capture
+  i = j
+  j = k
+  !$omp end atomic
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicCapture
+  ! CHECK-NOT: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> Relaxed
+  !$omp atomic capture relaxed
+  i = j
+  j = k
+  !$omp end atomic
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicCapture
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  !$omp atomic capture
+  i = j
+  j = k
+  !$omp end atomic
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicWrite
+  ! CHECK-NOT: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> Relaxed
+  !$omp atomic relaxed write
+  i = j
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicWrite
+  ! CHECK-NOT: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> Relaxed
+  !$omp atomic write relaxed
+  i = j
+
+  ! CHECK-LABEL: OpenMPAtomicConstruct -> OmpAtomicWrite
+  ! CHECK: OmpMemoryOrderClause -> OmpClause -> SeqCst
+  !$omp atomic write
+  i = j
+end program requires
diff --git a/flang/test/Semantics/OpenMP/requires01.f90 b/flang/test/Semantics/OpenMP/requires01.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/requires01.f90
@@ -0,0 +1,17 @@
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+! OpenMP Version 5.0
+! 2.4 Requires directive
+! All atomic_default_mem_order clauses in 'requires' directives found within a
+! compilation unit must specify the same ordering.
+
+!ERROR: Conflicting 'ATOMIC_DEFAULT_MEM_ORDER' REQUIRES clauses found in compilation unit
+program main
+  contains
+  subroutine f
+    !$omp requires atomic_default_mem_order(seq_cst)
+  end subroutine f
+
+  subroutine g
+    !$omp requires atomic_default_mem_order(relaxed)
+  end subroutine g
+end program
diff --git a/flang/test/Semantics/OpenMP/requires02.f90 b/flang/test/Semantics/OpenMP/requires02.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/requires02.f90
@@ -0,0 +1,17 @@
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+! OpenMP Version 5.0
+! 2.4 Requires directive
+! All atomic_default_mem_order clauses in 'requires' directives must come
+! strictly before any atomic directives on which the memory_order clause is not
+! specified.
+
+subroutine f
+  integer :: a = 0
+  !$omp atomic
+  a = a + 1
+end subroutine f
+
+subroutine g
+  !ERROR: 'ATOMIC_DEFAULT_MEM_ORDER' REQUIRES clause found lexically after atomic operation with the 'MEMORY_ORDER' clause not defined
+  !$omp requires atomic_default_mem_order(relaxed)
+end subroutine g
diff --git a/flang/test/Semantics/OpenMP/requires03.f90 b/flang/test/Semantics/OpenMP/requires03.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/requires03.f90
@@ -0,0 +1,21 @@
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+! OpenMP Version 5.0
+! 2.4 Requires directive
+! Target-related clauses in 'requires' directives must come strictly before any
+! device constructs, such as target regions.
+
+subroutine f
+  !$omp target
+  !$omp end target
+end subroutine f
+
+subroutine g
+  !ERROR: 'DYNAMIC_ALLOCATORS' REQUIRES clause found lexically after device construct
+  !$omp requires dynamic_allocators
+  !ERROR: 'REVERSE_OFFLOAD' REQUIRES clause found lexically after device construct
+  !$omp requires reverse_offload
+  !ERROR: 'UNIFIED_ADDRESS' REQUIRES clause found lexically after device construct
+  !$omp requires unified_address
+  !ERROR: 'UNIFIED_SHARED_MEMORY' REQUIRES clause found lexically after device construct
+  !$omp requires unified_shared_memory
+end subroutine g
diff --git a/flang/test/Semantics/OpenMP/requires04.f90 b/flang/test/Semantics/OpenMP/requires04.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/requires04.f90
@@ -0,0 +1,20 @@
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+! OpenMP Version 5.0
+! 2.4 Requires directive
+! Target-related clauses in 'requires' directives must come strictly before any
+! device constructs, such as declare target with device_type=nohost|any.
+
+subroutine f
+  !$omp declare target device_type(nohost)
+end subroutine f
+
+subroutine g
+  !ERROR: 'DYNAMIC_ALLOCATORS' REQUIRES clause found lexically after device construct
+  !$omp requires dynamic_allocators
+  !ERROR: 'REVERSE_OFFLOAD' REQUIRES clause found lexically after device construct
+  !$omp requires reverse_offload
+  !ERROR: 'UNIFIED_ADDRESS' REQUIRES clause found lexically after device construct
+  !$omp requires unified_address
+  !ERROR: 'UNIFIED_SHARED_MEMORY' REQUIRES clause found lexically after device construct
+  !$omp requires unified_shared_memory
+end subroutine g
diff --git a/flang/test/Semantics/OpenMP/requires05.f90 b/flang/test/Semantics/OpenMP/requires05.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/requires05.f90
@@ -0,0 +1,20 @@
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+! OpenMP Version 5.0
+! 2.4 Requires directive
+! Target-related clauses in 'requires' directives must come strictly before any
+! device constructs, such as declare target with 'to' clause and no device_type.
+
+subroutine f
+  !$omp declare target to(f)
+end subroutine f
+
+subroutine g
+  !ERROR: 'DYNAMIC_ALLOCATORS' REQUIRES clause found lexically after device construct
+  !$omp requires dynamic_allocators
+  !ERROR: 'REVERSE_OFFLOAD' REQUIRES clause found lexically after device construct
+  !$omp requires reverse_offload
+  !ERROR: 'UNIFIED_ADDRESS' REQUIRES clause found lexically after device construct
+  !$omp requires unified_address
+  !ERROR: 'UNIFIED_SHARED_MEMORY' REQUIRES clause found lexically after device construct
+  !$omp requires unified_shared_memory
+end subroutine g
diff --git a/flang/test/Semantics/OpenMP/requires06.f90 b/flang/test/Semantics/OpenMP/requires06.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/requires06.f90
@@ -0,0 +1,20 @@
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+! OpenMP Version 5.0
+! 2.4 Requires directive
+! Target-related clauses in 'requires' directives must come strictly before any
+! device constructs, such as declare target with extended list.
+
+subroutine f
+  !$omp declare target (f)
+end subroutine f
+
+subroutine g
+  !ERROR: 'DYNAMIC_ALLOCATORS' REQUIRES clause found lexically after device construct
+  !$omp requires dynamic_allocators
+  !ERROR: 'REVERSE_OFFLOAD' REQUIRES clause found lexically after device construct
+  !$omp requires reverse_offload
+  !ERROR: 'UNIFIED_ADDRESS' REQUIRES clause found lexically after device construct
+  !$omp requires unified_address
+  !ERROR: 'UNIFIED_SHARED_MEMORY' REQUIRES clause found lexically after device construct
+  !$omp requires unified_shared_memory
+end subroutine g
diff --git a/flang/test/Semantics/OpenMP/requires07.f90 b/flang/test/Semantics/OpenMP/requires07.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/requires07.f90
@@ -0,0 +1,13 @@
+! RUN: rm -rf %t && mkdir %t
+! RUN: %flang_fc1 -fsyntax-only -fopenmp -module-dir %t '%S/../Inputs/requires_module.f90'
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp -module-dir %t
+! OpenMP Version 5.0
+! 2.4 Requires directive
+! All atomic_default_mem_order clauses in 'requires' directives found within a
+! compilation unit must specify the same ordering. Test that this is propagated
+! from imported modules
+
+!ERROR: Conflicting 'ATOMIC_DEFAULT_MEM_ORDER' REQUIRES clauses found in compilation unit
+use requires_module
+!$omp requires atomic_default_mem_order(relaxed)
+end program