diff --git a/src/proto/streams/send.rs b/src/proto/streams/send.rs
index 207ce3f..32d6fd9 100644
--- a/src/proto/streams/send.rs
+++ b/src/proto/streams/send.rs
@@ -159,14 +159,56 @@ impl<B> Send<B> where B: Buf {
     {
         self.prioritize.recv_window_update(frame)?;
 
-        // TODO: If there is available connection capacity, release pending
-        // streams.
-        //
+        // Get the current connection capacity
+        let connection = self.prioritize.available_window();
+
         // Walk each stream pending capacity and see if this change to the
         // connection window can increase the advertised capacity of the stream.
+        //
+        // TODO: This is not a hugely efficient operation. It could be better to
+        // change the pending_capacity structure to a red-black tree.
+        //
+        self.pending_capacity.retain::<stream::NextCapacity, _>(
+            store,
+            |stream| {
+                // Make sure that the stream is flagged as queued
+                debug_assert!(stream.is_pending_send_capacity);
 
-        unimplemented!();
-        // Ok(())
+                // Get the current unadvertised window
+                let unadvertised = stream.unadvertised_send_window;
+
+                if unadvertised == 0 {
+                    stream.is_pending_send_capacity = false;
+                    return false;
+                }
+
+                let effective_window_size = match stream.state.send_flow_control() {
+                    Some(flow) => flow.effective_window_size(),
+                    None => {
+                        // The state transitioned and this stream is no longer
+                        // waiting for updates
+                        stream.is_pending_send_capacity = false;
+                        return false;
+                    }
+                };
+
+                if connection <= effective_window_size - unadvertised {
+                    // The window is not increased, but we remain interested in
+                    // updates in the future.
+                    return true;
+                }
+
+                if connection >= effective_window_size {
+                    stream.unadvertised_send_window = 0;
+                } else {
+                    stream.unadvertised_send_window = effective_window_size - connection;
+                }
+
+                stream.notify_send();
+                true
+            });
+
+        Ok(())
     }
 
     pub fn recv_stream_window_update(&mut self,
diff --git a/src/proto/streams/store.rs b/src/proto/streams/store.rs
index 2ade9c9..55b1229 100644
--- a/src/proto/streams/store.rs
+++ b/src/proto/streams/store.rs
@@ -32,9 +32,9 @@ pub(super) struct List<B> {
 pub(super) trait Next {
     fn next<B>(stream: &Stream<B>) -> Option<Key>;
 
-    fn set_next<B>(stream: &mut Stream<B>, key: Key);
+    fn set_next<B>(stream: &mut Stream<B>, key: Option<Key>);
 
-    fn take_next<B>(stream: &mut Stream<B>) -> Key;
+    fn take_next<B>(stream: &mut Stream<B>) -> Option<Key>;
 }
 
 /// A linked list
@@ -125,6 +125,20 @@ impl<B> Store<B> {
     }
 }
 
+impl<B> ops::Index<Key> for Store<B> {
+    type Output = Stream<B>;
+
+    fn index(&self, key: Key) -> &Self::Output {
+        self.slab.index(key.0)
+    }
+}
+
+impl<B> ops::IndexMut<Key> for Store<B> {
+    fn index_mut(&mut self, key: Key) -> &mut Self::Output {
+        self.slab.index_mut(key.0)
+    }
+}
+
 // ===== impl List =====
 
 impl<B> List<B> {
@@ -157,7 +171,7 @@ impl<B> List<B> {
             Some(ref mut idxs) => {
                 // Update the current tail node to point to `stream`
                 let key = stream.key();
-                N::set_next(&mut stream.resolve(idxs.tail), key);
+                N::set_next(&mut stream.resolve(idxs.tail), Some(key));
 
                 // Update the tail pointer
                 idxs.tail = stream.key();
@@ -181,7 +195,7 @@ impl<B> List<B> {
                 assert!(N::next(&*stream).is_none());
                 self.indices = None;
             } else {
-                idxs.head = N::take_next(&mut *stream);
+                idxs.head = N::take_next(&mut *stream).unwrap();
                 self.indices = Some(idxs);
             }
 
@@ -190,6 +204,53 @@ impl<B> List<B> {
 
         None
     }
+
+    pub fn retain<N, F>(&mut self, store: &mut Store<B>, mut f: F)
+        where N: Next,
+              F: FnMut(&mut Stream<B>) -> bool,
+    {
+        if let Some(mut idxs) = self.indices {
+            let mut prev = None;
+            let mut curr = idxs.head;
+
+            loop {
+                if f(&mut store[curr]) {
+                    // Element is retained, walk to the next
+                    if let Some(next) = N::next(&mut store[curr]) {
+                        prev = Some(curr);
+                        curr = next;
+                    } else {
+                        // Tail
+                        break;
+                    }
+                } else {
+                    // Element is dropped
+                    if let Some(prev) = prev {
+                        let next = N::take_next(&mut store[curr]);
+                        N::set_next(&mut store[prev], next);
+
+                        // current is last element, but guaranteed to not be the
+                        // only one
+                        if next.is_none() {
+                            idxs.tail = prev;
+                            break;
+                        }
+                    } else {
+                        if let Some(next) = N::take_next(&mut store[curr]) {
+                            curr = next;
+                            idxs.head = next;
+                        } else {
+                            // Only element
+                            self.indices = None;
+                            return;
+                        }
+                    }
+                }
+            }
+
+            self.indices = Some(idxs);
+        }
+    }
 }
 
 // ===== impl Ptr =====
diff --git a/src/proto/streams/stream.rs b/src/proto/streams/stream.rs
index 0c3ae1c..6f328c7 100644
--- a/src/proto/streams/stream.rs
+++ b/src/proto/streams/stream.rs
@@ -97,13 +97,12 @@ impl store::Next for Next {
         stream.next
     }
 
-    fn set_next<B>(stream: &mut Stream<B>, key: store::Key) {
-        debug_assert!(stream.next.is_none());
-        stream.next = Some(key);
+    fn set_next<B>(stream: &mut Stream<B>, key: Option<store::Key>) {
+        stream.next = key;
     }
 
-    fn take_next<B>(stream: &mut Stream<B>) -> store::Key {
-        stream.next.take().unwrap()
+    fn take_next<B>(stream: &mut Stream<B>) -> Option<store::Key> {
+        stream.next.take()
     }
 }
 
@@ -112,12 +111,11 @@ impl store::Next for NextCapacity {
         stream.next_capacity
     }
 
-    fn set_next<B>(stream: &mut Stream<B>, key: store::Key) {
-        debug_assert!(stream.next_capacity.is_none());
-        stream.next_capacity = Some(key);
+    fn set_next<B>(stream: &mut Stream<B>, key: Option<store::Key>) {
+        stream.next_capacity = key;
     }
 
-    fn take_next<B>(stream: &mut Stream<B>) -> store::Key {
-        stream.next_capacity.take().unwrap()
+    fn take_next<B>(stream: &mut Stream<B>) -> Option<store::Key> {
+        stream.next_capacity.take()
     }
 }