diff --git a/protos/google/protobuf/csharp_options.proto b/protos/google/protobuf/csharp_options.proto
index b58a549172..8a27046e59 100644
--- a/protos/google/protobuf/csharp_options.proto
+++ b/protos/google/protobuf/csharp_options.proto
@@ -5,12 +5,36 @@ import "google/protobuf/descriptor.proto";
 package google.protobuf;
 
 message CSharpFileOptions {
+
+  // Namespace for generated classes; defaults to the package.
   optional string namespace = 1;
+  
+  // Name of the "umbrella" class used for metadata about all
+  // the messages within this file. Default is based on the name
+  // of the file.
   optional string umbrella_classname = 2;
+  
+  // Whether classes should be public (true) or internal (false)
   optional bool public_classes = 3 [default = true];
+
+  // Whether to generate a single file for everything within the
+  // .proto file (false), or one file per message (true).
+  // This option is not currently honored; please log a feature
+  // request if you really want it.
   optional bool multiple_files = 4;
+
+  // Whether to nest messages within a single umbrella class (true)
+  // or create the umbrella class as a peer, with messages as
+  // top-level classes in the namespace (false)
   optional bool nest_classes = 5;
+  
+  // Generate appropriate support for Code Contracts
+  // (Ongoing; support should improve over time)
   optional bool code_contracts = 6;
+  
+  // Create subdirectories for namespaces, e.g. namespace "Foo.Bar"
+  // would generate files within [output directory]/Foo/Bar
+  optional bool expand_namespace_directories = 7;
 }
 
 extend FileOptions {
diff --git a/src/ProtoGen/Generator.cs b/src/ProtoGen/Generator.cs
index 9c0771ee8e..7e48ad672f 100644
--- a/src/ProtoGen/Generator.cs
+++ b/src/ProtoGen/Generator.cs
@@ -82,12 +82,29 @@ namespace Google.ProtocolBuffers.ProtoGen {
     /// </summary>
     private void Generate(FileDescriptor descriptor) {
       UmbrellaClassGenerator ucg = new UmbrellaClassGenerator(descriptor);
-      using (TextWriter textWriter = File.CreateText(Path.Combine(options.OutputDirectory, descriptor.CSharpOptions.UmbrellaClassname + ".cs"))) {
-        TextGenerator writer = new TextGenerator(textWriter);        
+      using (TextWriter textWriter = File.CreateText(GetOutputFile(descriptor))) {
+        TextGenerator writer = new TextGenerator(textWriter);
         ucg.Generate(writer);
       }
     }
 
+    private string GetOutputFile(FileDescriptor descriptor) {
+      CSharpFileOptions fileOptions = descriptor.CSharpOptions;
+      string filename = descriptor.CSharpOptions.UmbrellaClassname + ".cs";
+      string outputDirectory = options.OutputDirectory;
+      if (fileOptions.ExpandNamespaceDirectories) {
+        string package = fileOptions.Namespace;
+        if (!string.IsNullOrEmpty(package)) {
+          string[] bits = package.Split('.');
+          foreach (string bit in bits) {
+            outputDirectory = Path.Combine(outputDirectory, bit);
+          }
+          Directory.CreateDirectory(outputDirectory);
+        }
+      }
+      return Path.Combine(outputDirectory, filename);
+    }
+
     /// <summary>
     /// Resolves any dependencies and converts FileDescriptorProtos into FileDescriptors.
     /// The list returned is in the same order as the protos are listed in the descriptor set.
diff --git a/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs b/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
index 9ab99dfe32..b589a60ce7 100644
--- a/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
+++ b/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
@@ -37,22 +37,22 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       byte[] descriptorData = global::System.Convert.FromBase64String(
           "CiRnb29nbGUvcHJvdG9idWYvY3NoYXJwX29wdGlvbnMucHJvdG8SD2dvb2ds" + 
           "ZS5wcm90b2J1ZhogZ29vZ2xlL3Byb3RvYnVmL2Rlc2NyaXB0b3IucHJvdG8i" + 
-          "pgEKEUNTaGFycEZpbGVPcHRpb25zEhEKCW5hbWVzcGFjZRgBIAEoCRIaChJ1" + 
+          "zAEKEUNTaGFycEZpbGVPcHRpb25zEhEKCW5hbWVzcGFjZRgBIAEoCRIaChJ1" + 
           "bWJyZWxsYV9jbGFzc25hbWUYAiABKAkSHAoOcHVibGljX2NsYXNzZXMYAyAB" + 
           "KAg6BHRydWUSFgoObXVsdGlwbGVfZmlsZXMYBCABKAgSFAoMbmVzdF9jbGFz" + 
-          "c2VzGAUgASgIEhYKDmNvZGVfY29udHJhY3RzGAYgASgIIisKEkNTaGFycEZp" + 
-          "ZWxkT3B0aW9ucxIVCg1wcm9wZXJ0eV9uYW1lGAEgASgJOl4KE2NzaGFycF9m" + 
-          "aWxlX29wdGlvbnMSHC5nb29nbGUucHJvdG9idWYuRmlsZU9wdGlvbnMY6Acg" + 
-          "ASgLMiIuZ29vZ2xlLnByb3RvYnVmLkNTaGFycEZpbGVPcHRpb25zOmEKFGNz" + 
-          "aGFycF9maWVsZF9vcHRpb25zEh0uZ29vZ2xlLnByb3RvYnVmLkZpZWxkT3B0" + 
-          "aW9ucxjoByABKAsyIy5nb29nbGUucHJvdG9idWYuQ1NoYXJwRmllbGRPcHRp" + 
-          "b25z");
+          "c2VzGAUgASgIEhYKDmNvZGVfY29udHJhY3RzGAYgASgIEiQKHGV4cGFuZF9u" + 
+          "YW1lc3BhY2VfZGlyZWN0b3JpZXMYByABKAgiKwoSQ1NoYXJwRmllbGRPcHRp" + 
+          "b25zEhUKDXByb3BlcnR5X25hbWUYASABKAk6XgoTY3NoYXJwX2ZpbGVfb3B0" + 
+          "aW9ucxIcLmdvb2dsZS5wcm90b2J1Zi5GaWxlT3B0aW9ucxjoByABKAsyIi5n" + 
+          "b29nbGUucHJvdG9idWYuQ1NoYXJwRmlsZU9wdGlvbnM6YQoUY3NoYXJwX2Zp" + 
+          "ZWxkX29wdGlvbnMSHS5nb29nbGUucHJvdG9idWYuRmllbGRPcHRpb25zGOgH" + 
+          "IAEoCzIjLmdvb2dsZS5wcm90b2J1Zi5DU2hhcnBGaWVsZE9wdGlvbnM=");
       pbd::FileDescriptor.InternalDescriptorAssigner assigner = delegate(pbd::FileDescriptor root) {
         descriptor = root;
         internal__static_google_protobuf_CSharpFileOptions__Descriptor = Descriptor.MessageTypes[0];
         internal__static_google_protobuf_CSharpFileOptions__FieldAccessorTable = 
             new pb::FieldAccess.FieldAccessorTable<global::Google.ProtocolBuffers.DescriptorProtos.CSharpFileOptions, global::Google.ProtocolBuffers.DescriptorProtos.CSharpFileOptions.Builder>(internal__static_google_protobuf_CSharpFileOptions__Descriptor,
-                new string[] { "Namespace", "UmbrellaClassname", "PublicClasses", "MultipleFiles", "NestClasses", "CodeContracts", });
+                new string[] { "Namespace", "UmbrellaClassname", "PublicClasses", "MultipleFiles", "NestClasses", "CodeContracts", "ExpandNamespaceDirectories", });
         internal__static_google_protobuf_CSharpFieldOptions__Descriptor = Descriptor.MessageTypes[1];
         internal__static_google_protobuf_CSharpFieldOptions__FieldAccessorTable = 
             new pb::FieldAccess.FieldAccessorTable<global::Google.ProtocolBuffers.DescriptorProtos.CSharpFieldOptions, global::Google.ProtocolBuffers.DescriptorProtos.CSharpFieldOptions.Builder>(internal__static_google_protobuf_CSharpFieldOptions__Descriptor,
@@ -152,6 +152,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       get { return codeContracts_; }
     }
     
+    public const int ExpandNamespaceDirectoriesFieldNumber = 7;
+    private bool hasExpandNamespaceDirectories;
+    private bool expandNamespaceDirectories_ = false;
+    public bool HasExpandNamespaceDirectories {
+      get { return hasExpandNamespaceDirectories; }
+    }
+    public bool ExpandNamespaceDirectories {
+      get { return expandNamespaceDirectories_; }
+    }
+    
     public override bool IsInitialized {
       get {
         return true;
@@ -177,6 +187,9 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       if (HasCodeContracts) {
         output.WriteBool(6, CodeContracts);
       }
+      if (HasExpandNamespaceDirectories) {
+        output.WriteBool(7, ExpandNamespaceDirectories);
+      }
       UnknownFields.WriteTo(output);
     }
     
@@ -205,6 +218,9 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         if (HasCodeContracts) {
           size += pb::CodedOutputStream.ComputeBoolSize(6, CodeContracts);
         }
+        if (HasExpandNamespaceDirectories) {
+          size += pb::CodedOutputStream.ComputeBoolSize(7, ExpandNamespaceDirectories);
+        }
         size += UnknownFields.SerializedSize;
         memoizedSerializedSize = size;
         return size;
@@ -315,6 +331,9 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         if (other.HasCodeContracts) {
           CodeContracts = other.CodeContracts;
         }
+        if (other.HasExpandNamespaceDirectories) {
+          ExpandNamespaceDirectories = other.ExpandNamespaceDirectories;
+        }
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
@@ -371,6 +390,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
               CodeContracts = input.ReadBool();
               break;
             }
+            case 56: {
+              ExpandNamespaceDirectories = input.ReadBool();
+              break;
+            }
           }
         }
       }
@@ -485,6 +508,24 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         result.codeContracts_ = false;
         return this;
       }
+      
+      public bool HasExpandNamespaceDirectories {
+        get { return result.HasExpandNamespaceDirectories; }
+      }
+      public bool ExpandNamespaceDirectories {
+        get { return result.ExpandNamespaceDirectories; }
+        set { SetExpandNamespaceDirectories(value); }
+      }
+      public Builder SetExpandNamespaceDirectories(bool value) {
+        result.hasExpandNamespaceDirectories = true;
+        result.expandNamespaceDirectories_ = value;
+        return this;
+      }
+      public Builder ClearExpandNamespaceDirectories() {
+        result.hasExpandNamespaceDirectories = false;
+        result.expandNamespaceDirectories_ = false;
+        return this;
+      }
     }
     static CSharpFileOptions() {
       object.ReferenceEquals(global::Google.ProtocolBuffers.DescriptorProtos.CSharpOptions.Descriptor, null);