diff --git a/ipc.cc b/ipc.cc
index 9df2e21e..1adecab7 100644
--- a/ipc.cc
+++ b/ipc.cc
@@ -270,7 +270,7 @@ void IpcDirectionalChannel::PushMessage(IpcMessage* message) {
   if (payload_size == 0)
     return;
 
-  int partial_message_id = 0; // TODO
+  int partial_message_id = 0;
 
   std::cerr << "Starting dispatch of payload with size " << payload_size << std::endl;
   int count = 0;
diff --git a/src/message_queue.cc b/src/message_queue.cc
index 92798696..31609bf2 100644
--- a/src/message_queue.cc
+++ b/src/message_queue.cc
@@ -1,6 +1,93 @@
 #include "message_queue.h"
 
 #include <cassert>
+#include <functional>
+#include <iostream>
+#include <thread>
+
+#include "platform.h"
+
+namespace {
+
+const int kMinimumPartialPayloadSize = 128;
+
+struct BufferMessageIterator {
+  static BufferMessageIterator Begin(void* buffer, size_t bytes_used) {
+    if (bytes_used == 0)
+      return End();
+
+    return BufferMessageIterator(buffer, bytes_used);
+  }
+  static BufferMessageIterator End() {
+    return BufferMessageIterator(nullptr, 0);
+  }
+
+
+  // Start of buffer to iterate.
+  void* buffer;
+  // Number of bytes left in buffer to parse.
+  size_t remaining_bytes;
+
+  BufferMessageIterator(void* buffer, size_t remaining_bytes)
+    : buffer(buffer), remaining_bytes(remaining_bytes) {}
+
+  Message* get() const {
+    assert(buffer);
+    return reinterpret_cast<Message*>(buffer);
+  }
+  Message* operator*() const { return get(); }
+  Message* operator->() const { return get(); }
+
+  void operator++() {
+    size_t next_message_offset = get()->total_size;
+    if (next_message_offset >= remaining_bytes) {
+      assert(next_message_offset == remaining_bytes);
+      buffer = nullptr;
+      remaining_bytes = 0;
+      return;
+    }
+
+    buffer = reinterpret_cast<char*>(buffer) + next_message_offset;
+    remaining_bytes -= next_message_offset;
+  }
+
+  bool operator==(const BufferMessageIterator& other) const {
+    return buffer == other.buffer && remaining_bytes == other.remaining_bytes;
+  }
+  bool operator!=(const BufferMessageIterator& other) const {
+    return !(*this == other);
+  }
+};
+
+enum class RepeatResult {
+  RunAgain,
+  Break
+};
+
+// Run |action| an arbitrary number of times.
+void Repeat(std::function<RepeatResult()> action) {
+  bool first = true;
+  int log_iteration_count = 0;
+  int log_count = 0;
+  while (true) {
+    if (!first) {
+      if (log_iteration_count > 1000) {
+        log_iteration_count = 0;
+        std::cerr << "[info]: shmem full, waiting (" << log_count++ << ")" << std::endl; // TODO: remove
+      }
+      ++log_iteration_count;
+      // TODO: See if we can figure out a way to use condition variables cross-process.
+      std::this_thread::sleep_for(std::chrono::microseconds(0));
+    }
+    first = false;
+
+    if (action() == RepeatResult::RunAgain)
+      continue;
+    break;
+  }
+}
+
+}  // namespace
 
 struct MessageQueue::BufferMetadata {
   // Total number of used bytes exluding the sizeof this metadata object.
@@ -17,18 +104,116 @@ struct MessageQueue::BufferMetadata {
   // include the sizeof the buffer metadata.
   size_t total_message_bytes() { return total_message_bytes_; }
 
- private:
+  int next_partial_message_id = 0;
+
+private:
   size_t total_message_bytes_ = 0;
 };
 
 MessageQueue::MessageQueue(std::unique_ptr<Buffer> buffer, bool buffer_has_data)
-    : buffer_(std::move(buffer)) {
+  : buffer_(std::move(buffer)) {
   if (!buffer_has_data)
     new (buffer_->data) BufferMetadata();
 }
 
-void MessageQueue::Enqueue(const Message& message) {}
+void MessageQueue::Enqueue(const Message& message) {
+  //BufferMessageIterator::Begin(first_message_in_buffer(), metadata()->total_message_bytes);
 
-MessageQueue::BufferMetadata* MessageQueue::Metadata() {
+  int partial_message_id = 0;
+
+  Repeat([&]() {
+    auto lock = buffer_->WaitForExclusiveAccess();
+
+    // We cannot find the entire payload in the buffer. We have to send chunks
+    // of it over time.
+    if (message.total_size >= BytesAvailableInBuffer()) {
+      // There's not enough room for our minimum payload size, so try again later.
+      if ((sizeof(Message) + kMinimumPartialPayloadSize) > BytesAvailableInBuffer())
+        return RepeatResult::RunAgain;
+
+      if (partial_message_id == 0)
+        partial_message_id = ++metadata()->next_partial_message_id; // note: pre-increment so we 1 as initial value
+
+
+      size_t sent_payload_size = BytesAvailableInBuffer() - sizeof(Message);
+      free_message_in_buffer()->CopyFrom(message);
+      metadata()->set_total_messages_byte_count(
+        metadata()->total_message_bytes() + sizeof(Message) + sent_payload_size);
+
+      //shared_buffer->free_message()->Setup(message->ipc_id, partial_message_id, true /*has_more_chunks*/, sent_payload_size, payload);
+      //shared_buffer->metadata()->bytes_used += sizeof(JsonMessage) + sent_payload_size;
+      //shared_buffer->free_message()->ipc_id = IpcId::Invalid; // Note: free_message() may be past writable memory.
+
+      if (count++ > 50) {
+        std::cerr << "x50 Sending partial message with payload_size=" << sent_payload_size << std::endl;
+        count = 0;
+      }
+
+      // Prepare for next time.
+      payload_size -= sent_payload_size;
+      payload += sent_payload_size;
+      return RepeatResult::RunAgain;
+    }
+
+    return RepeatResult::Break;
+
+#if false
+    assert(payload_size > 0);
+
+    // We cannot find the entire payload in the buffer. We
+    // have to send chunks of it over time.
+    if ((sizeof(JsonMessage) + payload_size) > shared_buffer->bytes_available()) {
+      if ((sizeof(JsonMessage) + kMinimumPartialPayloadSize) > shared_buffer->bytes_available())
+        return DispatchResult::RunAgain;
+
+      if (partial_message_id == 0)
+        partial_message_id = ++shared_buffer->metadata()->next_partial_message_id; // note: pre-increment so we 1 as initial value
+
+      size_t sent_payload_size = shared_buffer->bytes_available() - sizeof(JsonMessage);
+      shared_buffer->free_message()->Setup(message->ipc_id, partial_message_id, true /*has_more_chunks*/, sent_payload_size, payload);
+      shared_buffer->metadata()->bytes_used += sizeof(JsonMessage) + sent_payload_size;
+      //shared_buffer->free_message()->ipc_id = IpcId::Invalid; // Note: free_message() may be past writable memory.
+
+      if (count++ > 50) {
+        std::cerr << "x50 Sending partial message with payload_size=" << sent_payload_size << std::endl;
+        count = 0;
+    }
+
+      // Prepare for next time.
+      payload_size -= sent_payload_size;
+      payload += sent_payload_size;
+      return RepeatResult::RunAgain;
+  }
+    // The entire payload fits. Send it all now.
+    else {
+      // Include partial message id, as there could have been previous parts of this payload.
+      shared_buffer->free_message()->Setup(message->ipc_id, partial_message_id, false /*has_more_chunks*/, payload_size, payload);
+      shared_buffer->metadata()->bytes_used += sizeof(JsonMessage) + payload_size;
+      shared_buffer->free_message()->ipc_id = IpcId::Invalid;
+      //std::cerr << "Sending full message with payload_size=" << payload_size << std::endl;
+
+      return RepeatResult::Break;
+    }
+#endif
+});
+}
+
+MessageQueue::BufferMetadata* MessageQueue::metadata() const {
   return reinterpret_cast<BufferMetadata*>(buffer_->data);
+}
+
+size_t MessageQueue::BytesAvailableInBuffer() const {
+  return buffer_->capacity - metadata()->total_bytes_used_including_metadata();
+}
+
+Message* MessageQueue::first_message_in_buffer() const {
+  return reinterpret_cast<Message*>(
+    reinterpret_cast<uint8_t>(buffer_->data) + sizeof(BufferMetadata));
+}
+
+Message* MessageQueue::free_message_in_buffer() const {
+  if (metadata()->total_bytes_used_including_metadata >= buffer_->capacity)
+    return nullptr;
+  return reinterpret_cast<Message*>(
+    reinterpret_cast<uint8_t>(buffer_->data) + metadata()->total_bytes_used_including_metadata());
 }
\ No newline at end of file
diff --git a/src/message_queue.h b/src/message_queue.h
index 183e2e9e..e2ab030e 100644
--- a/src/message_queue.h
+++ b/src/message_queue.h
@@ -11,6 +11,9 @@ struct Message {
 
   // Total size of the message (including metadata that this object stores).
   size_t total_size;
+
+  // Size of the extra message data immediately following the message payload.
+  size_t message_size() const { return total_size - sizeof(Message); }
 };
 
 // A MessageQueue is a FIFO container storing messages in an arbitrary memory
@@ -55,7 +58,12 @@ struct MessageQueue {
  private:
   struct BufferMetadata;
 
-  BufferMetadata* Metadata();
+  BufferMetadata* metadata() const;
+  // Returns the number of bytes currently available in the buffer.
+  size_t BytesAvailableInBuffer() const;
+  Message* first_message_in_buffer() const;
+  // First free message in the buffer.
+  Message* free_message_in_buffer() const;
 
   std::unique_ptr<Buffer> buffer_;
 };