diff --git a/common/BUILD b/common/BUILD
index 213a91035..1007f85dd 100644
--- a/common/BUILD
+++ b/common/BUILD
@@ -1035,8 +1035,10 @@ cc_library(
         "function_descriptor.h",
     ],
     deps = [
+        ":ast",
         ":kind",
         "@com_google_absl//absl/base:core_headers",
+        "@com_google_absl//absl/functional:overload",
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/types:span",
     ],
diff --git a/common/function_descriptor.cc b/common/function_descriptor.cc
index 779fe939b..a48f9c211 100644
--- a/common/function_descriptor.cc
+++ b/common/function_descriptor.cc
@@ -16,9 +16,14 @@
 
 #include <algorithm>
 #include <cstddef>
+#include <memory>
+#include <variant>
+#include <vector>
 
 #include "absl/base/macros.h"
+#include "absl/functional/overload.h"
 #include "absl/types/span.h"
+#include "common/ast.h"
 #include "common/kind.h"
 
 namespace cel {
@@ -90,4 +95,86 @@ bool FunctionDescriptor::operator<(const FunctionDescriptor& other) const {
   return false;
 }
 
+namespace {
+
+[[nodiscard]]
+Kind TypeSpecToKind(const TypeSpec& spec) {
+  return std::visit(
+      absl::Overload(
+          [](UnsetTypeSpec) -> Kind { return Kind::kError; },
+          [](const DynTypeSpec& spec) -> Kind { return Kind::kDyn; },
+          [](const NullTypeSpec& spec) -> Kind { return Kind::kNull; },
+          [](const PrimitiveType& spec) -> Kind {
+            switch (spec) {
+              case PrimitiveType::kPrimitiveTypeUnspecified:
+                return Kind::kError;
+              case PrimitiveType::kBool:
+                return Kind::kBool;
+              case PrimitiveType::kInt64:
+                return Kind::kInt;
+              case PrimitiveType::kUint64:
+                return Kind::kUint;
+              case PrimitiveType::kDouble:
+                return Kind::kDouble;
+              case PrimitiveType::kString:
+                return Kind::kString;
+              case PrimitiveType::kBytes:
+                return Kind::kBytes;
+            }
+          },
+          [](const PrimitiveTypeWrapper& spec) -> Kind {
+            switch (spec.type()) {
+              case PrimitiveType::kPrimitiveTypeUnspecified:
+                return Kind::kError;
+              case PrimitiveType::kBool:
+                return Kind::kBoolWrapper;
+              case PrimitiveType::kInt64:
+                return Kind::kIntWrapper;
+              case PrimitiveType::kUint64:
+                return Kind::kUintWrapper;
+              case PrimitiveType::kDouble:
+                return Kind::kDoubleWrapper;
+              case PrimitiveType::kString:
+                return Kind::kStringWrapper;
+              case PrimitiveType::kBytes:
+                return Kind::kBytesWrapper;
+            }
+          },
+          [](const WellKnownTypeSpec& spec) -> Kind {
+            switch (spec) {
+              case cel::WellKnownTypeSpec::kWellKnownTypeUnspecified:
+                return Kind::kError;
+              case cel::WellKnownTypeSpec::kDuration:
+                return Kind::kError;
+              case cel::WellKnownTypeSpec::kTimestamp:
+                return Kind::kTimestamp;
+              case cel::WellKnownTypeSpec::kAny:
+                return Kind::kAny;
+            }
+          },
+          [](const ListTypeSpec& spec) -> Kind { return Kind::kList; },
+          [](const MapTypeSpec& spec) -> Kind { return Kind::kMap; },
+          [](const FunctionTypeSpec& spec) -> Kind { return Kind::kFunction; },
+          [](const MessageTypeSpec& spec) -> Kind { return Kind::kStruct; },
+          [](const ParamTypeSpec& spec) -> Kind { return Kind::kTypeParam; },
+          [](const std::unique_ptr<TypeSpec>& spec) -> Kind {
+            return Kind::kType;
+          },
+          [](const ErrorTypeSpec& spec) -> Kind { return Kind::kError; },
+          [](const AbstractType& spec) -> Kind { return Kind::kOpaque; }),
+      spec.type_kind());
+}
+
+}  // namespace
+
+std::vector<Kind> FunctionDescriptor::FunctionTypeSpecToArgumentKinds(
+    const FunctionTypeSpec& spec) {
+  std::vector<Kind> kinds;
+  kinds.reserve(spec.arg_types().size());
+  for (const auto& arg : spec.arg_types()) {
+    kinds.push_back(TypeSpecToKind(arg));
+  }
+  return kinds;
+}
+
 }  // namespace cel
diff --git a/common/function_descriptor.h b/common/function_descriptor.h
index 1c97bdcca..2f3b6ffc8 100644
--- a/common/function_descriptor.h
+++ b/common/function_descriptor.h
@@ -19,8 +19,10 @@
 #include <utility>
 #include <vector>
 
+#include "absl/base/attributes.h"
 #include "absl/strings/string_view.h"
 #include "absl/types/span.h"
+#include "common/ast.h"
 #include "common/kind.h"
 
 namespace cel {
@@ -42,8 +44,28 @@ struct FunctionDescriptorOptions {
 
 // Coarsely describes a function for the purpose of runtime resolution of
 // overloads.
-class FunctionDescriptor final {
+class FunctionDescriptor {
  public:
+  // Creates a FunctionDescriptor for a global function.
+  [[nodiscard]]
+  static FunctionDescriptor Global(absl::string_view name,
+                                   absl::string_view overload_id,
+                                   const FunctionTypeSpec& type,
+                                   FunctionDescriptorOptions options = {}) {
+    return FunctionDescriptor(name, overload_id, type, options,
+                              /*is_receiver_style=*/false);
+  }
+
+  // Creates a FunctionDescriptor for a member function.
+  [[nodiscard]]
+  static FunctionDescriptor Member(absl::string_view name,
+                                   absl::string_view overload_id,
+                                   const FunctionTypeSpec& type,
+                                   FunctionDescriptorOptions options = {}) {
+    return FunctionDescriptor(name, overload_id, type, options,
+                              /*is_receiver_style=*/true);
+  }
+
   FunctionDescriptor(const FunctionDescriptor&) = default;
   FunctionDescriptor(FunctionDescriptor&&) = default;
   FunctionDescriptor& operator=(const FunctionDescriptor&) = default;
@@ -67,20 +89,26 @@ class FunctionDescriptor final {
                      std::vector<Kind> types,
                      FunctionDescriptorOptions options = {})
       : name_(name),
-        types_(std::move(types)),
+        kinds_(std::move(types)),
         is_receiver_style_(is_receiver_style),
         options_(std::move(options)) {}
 
   // Function name.
   const std::string& name() const { return name_; }
 
+  // Function overload ID. This may be empty for legacy code.
+  [[nodiscard]]
+  absl::string_view overload_id() const ABSL_ATTRIBUTE_LIFETIME_BOUND {
+    return overload_id_;
+  }
+
   // Whether function is receiver style i.e. true means arg0.name(args[1:]...).
   bool receiver_style() const { return is_receiver_style_; }
 
   // The argument types the function accepts.
   //
   // TODO(uncreated-issue/17): make this kinds
-  const std::vector<Kind>& types() const { return types_; }
+  const std::vector<Kind>& types() const { return kinds_; }
 
   // if true (strict, default), error or unknown arguments are propagated
   // instead of calling the function. if false (non-strict), the function may
@@ -108,8 +136,22 @@ class FunctionDescriptor final {
   bool operator<(const FunctionDescriptor& other) const;
 
  private:
+  [[nodiscard]]
+  static std::vector<Kind> FunctionTypeSpecToArgumentKinds(
+      const FunctionTypeSpec& spec);
+
+  FunctionDescriptor(absl::string_view name, absl::string_view overload_id,
+                     const FunctionTypeSpec& type,
+                     FunctionDescriptorOptions options, bool is_receiver_style)
+      : name_(name),
+        overload_id_(overload_id),
+        kinds_(FunctionTypeSpecToArgumentKinds(type)),
+        is_receiver_style_(is_receiver_style),
+        options_(std::move(options)) {}
+
   std::string name_;
-  std::vector<Kind> types_;
+  std::string overload_id_;
+  std::vector<Kind> kinds_;
   bool is_receiver_style_;
   FunctionDescriptorOptions options_;
 };