diff --git a/reflect/protodesc/toproto.go b/reflect/protodesc/toproto.go
new file mode 100644
index 0000000..efe0572
--- /dev/null
+++ b/reflect/protodesc/toproto.go
@@ -0,0 +1,212 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+package protodesc
+
+import (
+	"fmt"
+
+	"github.com/golang/protobuf/v2/internal/encoding/defval"
+	"github.com/golang/protobuf/v2/internal/scalar"
+	"github.com/golang/protobuf/v2/reflect/protoreflect"
+	descriptorpb "github.com/golang/protobuf/v2/types/descriptor"
+)
+
+// ToFileDescriptorProto converts a FileDescriptor to a
+// google.protobuf.FileDescriptorProto.
+func ToFileDescriptorProto(file protoreflect.FileDescriptor) *descriptorpb.FileDescriptorProto {
+	p := &descriptorpb.FileDescriptorProto{
+		Name:    scalar.String(file.Path()),
+		Package: scalar.String(string(file.Package())),
+		// TODO: Clone options messages, or document this as aliasing.
+		Options: file.Options().(*descriptorpb.FileOptions),
+	}
+	for i, imports := 0, file.Imports(); i < imports.Len(); i++ {
+		imp := imports.Get(i)
+		p.Dependency = append(p.Dependency, imp.Path())
+		if imp.IsPublic {
+			p.PublicDependency = append(p.PublicDependency, int32(i))
+		}
+		if imp.IsWeak {
+			p.WeakDependency = append(p.WeakDependency, int32(i))
+		}
+	}
+	for i, messages := 0, file.Messages(); i < messages.Len(); i++ {
+		p.MessageType = append(p.MessageType, ToDescriptorProto(messages.Get(i)))
+	}
+	for i, enums := 0, file.Enums(); i < enums.Len(); i++ {
+		p.EnumType = append(p.EnumType, ToEnumDescriptorProto(enums.Get(i)))
+	}
+	for i, services := 0, file.Services(); i < services.Len(); i++ {
+		p.Service = append(p.Service, ToServiceDescriptorProto(services.Get(i)))
+	}
+	for i, exts := 0, file.Extensions(); i < exts.Len(); i++ {
+		p.Extension = append(p.Extension, ToFieldDescriptorProto(exts.Get(i)))
+	}
+	if syntax := file.Syntax(); syntax != protoreflect.Proto2 {
+		p.Syntax = scalar.String(file.Syntax().String())
+	}
+	return p
+}
+
+// ToDescriptorProto converts a MessageDescriptor to a
+// google.protobuf.DescriptorProto.
+func ToDescriptorProto(message protoreflect.MessageDescriptor) *descriptorpb.DescriptorProto {
+	p := &descriptorpb.DescriptorProto{
+		Name:    scalar.String(string(message.Name())),
+		Options: message.Options().(*descriptorpb.MessageOptions),
+	}
+	for i, fields := 0, message.Fields(); i < fields.Len(); i++ {
+		p.Field = append(p.Field, ToFieldDescriptorProto(fields.Get(i)))
+	}
+	for i, exts := 0, message.Extensions(); i < exts.Len(); i++ {
+		p.Extension = append(p.Extension, ToFieldDescriptorProto(exts.Get(i)))
+	}
+	for i, messages := 0, message.Messages(); i < messages.Len(); i++ {
+		p.NestedType = append(p.NestedType, ToDescriptorProto(messages.Get(i)))
+	}
+	for i, enums := 0, message.Enums(); i < enums.Len(); i++ {
+		p.EnumType = append(p.EnumType, ToEnumDescriptorProto(enums.Get(i)))
+	}
+	for i, xranges := 0, message.ExtensionRanges(); i < xranges.Len(); i++ {
+		xrange := xranges.Get(i)
+		p.ExtensionRange = append(p.ExtensionRange, &descriptorpb.DescriptorProto_ExtensionRange{
+			Start:   scalar.Int32(int32(xrange[0])),
+			End:     scalar.Int32(int32(xrange[1])),
+			Options: message.ExtensionRangeOptions(i).(*descriptorpb.ExtensionRangeOptions),
+		})
+	}
+	for i, oneofs := 0, message.Oneofs(); i < oneofs.Len(); i++ {
+		p.OneofDecl = append(p.OneofDecl, ToOneofDescriptorProto(oneofs.Get(i)))
+	}
+	for i, ranges := 0, message.ReservedRanges(); i < ranges.Len(); i++ {
+		rrange := ranges.Get(i)
+		p.ReservedRange = append(p.ReservedRange, &descriptorpb.DescriptorProto_ReservedRange{
+			Start: scalar.Int32(int32(rrange[0])),
+			End:   scalar.Int32(int32(rrange[1])),
+		})
+	}
+	for i, names := 0, message.ReservedNames(); i < names.Len(); i++ {
+		p.ReservedName = append(p.ReservedName, string(names.Get(i)))
+	}
+	return p
+}
+
+// ToFieldDescriptorProto converts a FieldDescriptor to a
+// google.protobuf.FieldDescriptorProto.
+func ToFieldDescriptorProto(field protoreflect.FieldDescriptor) *descriptorpb.FieldDescriptorProto {
+	p := &descriptorpb.FieldDescriptorProto{
+		Name:     scalar.String(string(field.Name())),
+		Number:   scalar.Int32(int32(field.Number())),
+		Label:    descriptorpb.FieldDescriptorProto_Label(field.Cardinality()).Enum(),
+		Type:     descriptorpb.FieldDescriptorProto_Type(field.Kind()).Enum(),
+		Extendee: fullNameOf(field.ExtendedType()),
+		Options:  field.Options().(*descriptorpb.FieldOptions),
+	}
+	switch field.Kind() {
+	case protoreflect.EnumKind:
+		p.TypeName = fullNameOf(field.EnumType())
+	case protoreflect.MessageKind, protoreflect.GroupKind:
+		p.TypeName = fullNameOf(field.MessageType())
+	}
+	if field.HasJSONName() {
+		p.JsonName = scalar.String(field.JSONName())
+	}
+	if field.HasDefault() {
+		if field.Kind() == protoreflect.EnumKind {
+			// TODO: defval.Marshal should probably take a FieldDescriptor
+			// instead of a Kind and do this itself.
+			p.DefaultValue = scalar.String(string(field.DefaultEnumValue().Name()))
+		} else {
+			def, err := defval.Marshal(field.Default(), field.Kind(), defval.Descriptor)
+			if err != nil {
+				panic(fmt.Sprintf("%v: %v", field.FullName(), err))
+			}
+			p.DefaultValue = scalar.String(def)
+		}
+	}
+	if oneof := field.OneofType(); oneof != nil {
+		p.OneofIndex = scalar.Int32(int32(oneof.Index()))
+	}
+	return p
+}
+
+// ToOneofDescriptorProto converts a OneofDescriptor to a
+// google.protobuf.OneofDescriptorProto.
+func ToOneofDescriptorProto(oneof protoreflect.OneofDescriptor) *descriptorpb.OneofDescriptorProto {
+	return &descriptorpb.OneofDescriptorProto{
+		Name:    scalar.String(string(oneof.Name())),
+		Options: oneof.Options().(*descriptorpb.OneofOptions),
+	}
+}
+
+// ToEnumDescriptorProto converts a EnumDescriptor to a
+// google.protobuf.EnumDescriptorProto.
+func ToEnumDescriptorProto(enum protoreflect.EnumDescriptor) *descriptorpb.EnumDescriptorProto {
+	p := &descriptorpb.EnumDescriptorProto{
+		Name:    scalar.String(string(enum.Name())),
+		Options: enum.Options().(*descriptorpb.EnumOptions),
+	}
+	for i, values := 0, enum.Values(); i < values.Len(); i++ {
+		p.Value = append(p.Value, ToEnumValueDescriptorProto(values.Get(i)))
+	}
+	for i, ranges := 0, enum.ReservedRanges(); i < ranges.Len(); i++ {
+		rrange := ranges.Get(i)
+		p.ReservedRange = append(p.ReservedRange, &descriptorpb.EnumDescriptorProto_EnumReservedRange{
+			Start: scalar.Int32(int32(rrange[0])),
+			End:   scalar.Int32(int32(rrange[1])),
+		})
+	}
+	for i, names := 0, enum.ReservedNames(); i < names.Len(); i++ {
+		p.ReservedName = append(p.ReservedName, string(names.Get(i)))
+	}
+	return p
+}
+
+// ToEnumValueDescriptorProto converts a EnumValueDescriptor to a
+// google.protobuf.EnumValueDescriptorProto.
+func ToEnumValueDescriptorProto(value protoreflect.EnumValueDescriptor) *descriptorpb.EnumValueDescriptorProto {
+	return &descriptorpb.EnumValueDescriptorProto{
+		Name:    scalar.String(string(value.Name())),
+		Number:  scalar.Int32(int32(value.Number())),
+		Options: value.Options().(*descriptorpb.EnumValueOptions),
+	}
+}
+
+// ToServiceDescriptorProto converts a ServiceDescriptor to a
+// google.protobuf.ServiceDescriptorProto.
+func ToServiceDescriptorProto(service protoreflect.ServiceDescriptor) *descriptorpb.ServiceDescriptorProto {
+	p := &descriptorpb.ServiceDescriptorProto{
+		Name:    scalar.String(string(service.Name())),
+		Options: service.Options().(*descriptorpb.ServiceOptions),
+	}
+	for i, methods := 0, service.Methods(); i < methods.Len(); i++ {
+		p.Method = append(p.Method, ToMethodDescriptorProto(methods.Get(i)))
+	}
+	return p
+}
+
+// ToMethodDescriptorProto converts a MethodDescriptor to a
+// google.protobuf.MethodDescriptorProto.
+func ToMethodDescriptorProto(method protoreflect.MethodDescriptor) *descriptorpb.MethodDescriptorProto {
+	p := &descriptorpb.MethodDescriptorProto{
+		Name:       scalar.String(string(method.Name())),
+		InputType:  fullNameOf(method.InputType()),
+		OutputType: fullNameOf(method.OutputType()),
+		Options:    method.Options().(*descriptorpb.MethodOptions),
+	}
+	if method.IsStreamingClient() {
+		p.ClientStreaming = scalar.Bool(true)
+	}
+	if method.IsStreamingServer() {
+		p.ServerStreaming = scalar.Bool(true)
+	}
+	return p
+}
+
+func fullNameOf(d protoreflect.Descriptor) *string {
+	if d == nil {
+		return nil
+	}
+	return scalar.String("." + string(d.FullName()))
+}