diff --git a/src/frame/mod.rs b/src/frame/mod.rs
index c31866c..a481d61 100644
--- a/src/frame/mod.rs
+++ b/src/frame/mod.rs
@@ -32,6 +32,7 @@ mod reset;
 mod settings;
 mod stream_id;
 mod util;
+mod window_update;
 
 pub use self::data::Data;
 pub use self::go_away::GoAway;
@@ -41,6 +42,7 @@ pub use self::ping::Ping;
 pub use self::reset::Reset;
 pub use self::settings::{Settings, SettingSet};
 pub use self::stream_id::StreamId;
+pub use self::window_update::WindowUpdate;
 
 // Re-export some constants
 pub use self::settings::{
@@ -56,7 +58,8 @@ pub enum Frame {
     Headers(Headers),
     PushPromise(PushPromise),
     Settings(Settings),
-    Ping(Ping)
+    Ping(Ping),
+    WindowUpdate(WindowUpdate)
 }
 
 /// Errors that can occur during parsing an HTTP/2 frame.
diff --git a/src/frame/window_update.rs b/src/frame/window_update.rs
new file mode 100644
index 0000000..92ec263
--- /dev/null
+++ b/src/frame/window_update.rs
@@ -0,0 +1,48 @@
+use StreamId;
+use byteorder::{ByteOrder, NetworkEndian};
+use bytes::{BufMut};
+use frame::{self, Head, Kind, Error};
+
+const INCREMENT_MASK: u32 = 1 << 31;
+
+type Increment = u32;
+
+#[derive(Debug)]
+pub struct WindowUpdate {
+    stream_id: StreamId,
+    increment: Increment,
+}
+
+impl WindowUpdate {
+    pub fn stream_id(&self) -> StreamId {
+        self.stream_id
+    }
+
+    pub fn increment(&self) -> Increment {
+        self.increment
+    }
+
+        /// Builds a `Ping` frame from a raw frame.
+    pub fn load(head: Head, bytes: &[u8]) -> Result<WindowUpdate, Error> {
+        debug_assert_eq!(head.kind(), ::frame::Kind::WindowUpdate);
+        Ok(WindowUpdate {
+            stream_id: head.stream_id(),
+            // Clear the most significant bit, as that is reserved and MUST be ignored when
+            // received.
+            increment: NetworkEndian::read_u32(bytes) & !INCREMENT_MASK,
+        })
+    }
+
+    pub fn encode<B: BufMut>(&self, dst: &mut B) {
+        trace!("encoding WINDOW_UPDATE; id={:?}", self.stream_id);
+        let head = Head::new(Kind::Ping, 0, self.stream_id);
+        head.encode(4, dst);
+        dst.put_u32::<NetworkEndian>(self.increment);
+    }
+}
+
+impl From<WindowUpdate> for frame::Frame {
+    fn from(src: WindowUpdate) -> frame::Frame {
+        frame::Frame::WindowUpdate(src)
+    }
+}
diff --git a/src/proto/connection.rs b/src/proto/connection.rs
index 0c4f888..e8e3c9d 100644
--- a/src/proto/connection.rs
+++ b/src/proto/connection.rs
@@ -1,7 +1,8 @@
-use {frame, Frame, ConnectionError, Peer, StreamId};
+use {Frame, ConnectionError, Peer, StreamId};
 use client::Client;
+use frame::{Frame as WireFrame};
 use server::Server;
-use proto::{self, ReadySink, State};
+use proto::{self, ReadySink, State, WindowUpdate};
 
 use tokio_io::{AsyncRead, AsyncWrite};
 
@@ -15,17 +16,60 @@ use fnv::FnvHasher;
 use std::marker::PhantomData;
 use std::hash::BuildHasherDefault;
 
+pub struct FlowControlViolation;
+
+#[derive(Debug)]
+struct FlowController {
+    window_size: u32,
+    underflow: u32,
+}
+
+impl FlowController {
+    pub fn new(window_size: u32) -> FlowController {
+        FlowController {
+            window_size,
+            underflow: 0,
+        }
+    }
+
+    pub fn shrink(&mut self, mut sz: u32) {
+        self.underflow += sz;
+    }
+
+    pub fn consume(&mut self, mut sz: u32) -> Result<(), FlowControlViolation> {
+        if sz < self.window_size {
+            self.underflow -= sz;
+            return Err(FlowControlViolation);
+        }
+
+        self.window_size -= sz;
+        Ok(())
+    }
+
+    pub fn increment(&mut self, mut sz: u32) {
+        if sz <= self.underflow {
+            self.underflow -= sz;
+            return;
+        }
+
+        sz -= self.underflow;
+        self.window_size += sz;
+    }
+}
+
 /// An H2 connection
 #[derive(Debug)]
 pub struct Connection<T, P> {
     inner: proto::Inner<T>,
     streams: StreamMap<State>,
     peer: PhantomData<P>,
+    local_flow_controller: FlowController,
+        remote_flow_controller: FlowController,
 }
 
 type StreamMap<T> = OrderMap<StreamId, T, BuildHasherDefault<FnvHasher>>;
 
-pub fn new<T, P>(transport: proto::Inner<T>) -> Connection<T, P>
+pub fn new<T, P>(transport: proto::Inner<T>, initial_local_window_size: u32, initial_remote_window_size: u32) -> Connection<T, P>
     where T: AsyncRead + AsyncWrite,
           P: Peer,
 {
@@ -33,15 +77,35 @@ pub fn new<T, P>(transport: proto::Inner<T>) -> Connection<T, P>
         inner: transport,
         streams: StreamMap::default(),
         peer: PhantomData,
+        local_flow_controller: FlowController::new(initial_local_window_size),
+        remote_flow_controller: FlowController::new(initial_remote_window_size),
     }
 }
 
 impl<T, P> Connection<T, P> {
-    pub fn increment_local_window_size(&mut self, id: StreamId, increment: usize) {
+    /// Publishes stream window updates to the remote.
+    ///
+    /// Connection window updates (StreamId=0) and stream window updates are published
+    /// distinctly.
+    pub fn increment_local_window(&mut self, up: WindowUpdate) {
+        let incr = up.increment();
+        let flow = match up {
+            WindowUpdate::Connection { .. } => Some(&self.local_flow_controller),
+            WindowUpdate::Stream { id, .. } => {
+                self.streams.get(&id).map(|s| s.local_flow_controller())
+            }
+        };
+        if let Some(flow) = flow {
+            flow.increment(incr);
+        }
         unimplemented!()
     }
 
-    pub fn poll_remote_window_size(&mut self, id: StreamId) -> Poll<usize, ()> {
+    /// Advertises stream window updates from the remote.
+    ///
+    /// Connection window updates (StreamId=0) and stream window updates are advertised
+    /// distinctly.
+    pub fn poll_remote_window(&mut self) -> Poll<WindowUpdate, ()> {
         unimplemented!()
     }
 }
@@ -88,8 +152,6 @@ impl<T, P> Stream for Connection<T, P>
     type Error = ConnectionError;
 
     fn poll(&mut self) -> Poll<Option<Self::Item>, ConnectionError> {
-        use frame::Frame::*;
-
         trace!("Connection::poll");
 
         let frame = match try!(self.inner.poll()) {
@@ -105,7 +167,7 @@ impl<T, P> Stream for Connection<T, P>
         trace!("received; frame={:?}", frame);
 
         let frame = match frame {
-            Some(Headers(v)) => {
+            Some(WireFrame::Headers(v)) => {
                 // TODO: Update stream state
                 let stream_id = v.stream_id();
                 let end_of_stream = v.is_end_stream();
@@ -130,7 +192,7 @@ impl<T, P> Stream for Connection<T, P>
                     end_of_stream: end_of_stream,
                 }
             }
-            Some(Data(v)) => {
+            Some(WireFrame::Data(v)) => {
                 // TODO: Validate frame
 
                 let stream_id = v.stream_id();
@@ -189,7 +251,7 @@ impl<T, P> Sink for Connection<T, P>
 
                 // We already ensured that the upstream can handle the frame, so
                 // panic if it gets rejected.
-                let res = try!(self.inner.start_send(frame::Frame::Headers(frame)));
+                let res = try!(self.inner.start_send(WireFrame::Headers(frame)));
 
                 // This is a one-way conversion. By checking `poll_ready` first,
                 // it's already been determined that the inner `Sink` can accept
diff --git a/src/proto/framed_read.rs b/src/proto/framed_read.rs
index ee476d4..b4d0db6 100644
--- a/src/proto/framed_read.rs
+++ b/src/proto/framed_read.rs
@@ -96,7 +96,10 @@ impl<T> FramedRead<T> {
                 debug!("decoded; frame={:?}", frame);
                 unimplemented!();
             }
-            Kind::WindowUpdate => unimplemented!(),
+            Kind::WindowUpdate => {
+                let frame = try!(frame::WindowUpdate::load(head, &bytes[frame::HEADER_LEN..]));
+                frame.into()
+            }
             Kind::Continuation => {
                 unimplemented!();
             }
diff --git a/src/proto/framed_write.rs b/src/proto/framed_write.rs
index 07bd934..8ece940 100644
--- a/src/proto/framed_write.rs
+++ b/src/proto/framed_write.rs
@@ -120,6 +120,10 @@ impl<T: AsyncWrite> Sink for FramedWrite<T> {
                 v.encode(self.buf.get_mut());
                 trace!("encoded ping; rem={:?}", self.buf.remaining());
             }
+            Frame::WindowUpdate(v) => {
+                v.encode(self.buf.get_mut());
+                trace!("encoded window_update; rem={:?}", self.buf.remaining());
+            }
         }
 
         Ok(AsyncSink::Ready)
diff --git a/src/proto/mod.rs b/src/proto/mod.rs
index 923a284..66df641 100644
--- a/src/proto/mod.rs
+++ b/src/proto/mod.rs
@@ -5,6 +5,7 @@ mod ping_pong;
 mod ready;
 mod settings;
 mod state;
+mod window_update;
 
 pub use self::connection::{Connection};
 pub use self::framed_read::FramedRead;
@@ -13,6 +14,7 @@ pub use self::ping_pong::PingPong;
 pub use self::ready::ReadySink;
 pub use self::settings::Settings;
 pub use self::state::State;
+pub use self::window_update::WindowUpdate;
 
 use {frame, Peer};
 
@@ -83,5 +85,5 @@ pub fn from_server_handshaker<T, P>(transport: Settings<FramedWrite<T>>)
     });
 
     // Finally, return the constructed `Connection`
-    connection::new(settings)
+    connection::new(settings, 65_535, 65_535)
 }
diff --git a/src/proto/window_update.rs b/src/proto/window_update.rs
new file mode 100644
index 0000000..e6ea78a
--- /dev/null
+++ b/src/proto/window_update.rs
@@ -0,0 +1,16 @@
+use StreamId;
+
+#[derive(Debug)]
+pub enum WindowUpdate {
+    Connection { increment: usize },
+    Stream { id: StreamId, increment: usize },
+}
+
+impl WindowUpdate {
+    pub fn increment(&self) -> usize {
+        match *self {
+            WindowUpdate::Connection { increment } |
+            WindowUpdate::Stream { increment, .. } => increment
+        }
+    }
+}