diff --git a/automerge-wasm/src/lib.rs b/automerge-wasm/src/lib.rs
index c4f3faeff..e0cc32f20 100644
--- a/automerge-wasm/src/lib.rs
+++ b/automerge-wasm/src/lib.rs
@@ -464,6 +464,13 @@ impl Automerge {
                     };
                 }
 
+                Patch::Increment { obj, key, value } => {
+                    js_set(&patch, "action", "increment")?;
+                    js_set(&patch, "obj", obj.to_string())?;
+                    js_set(&patch, "key", key)?;
+                    js_set(&patch, "value", value.0)?;
+                }
+
                 Patch::Delete { obj, key } => {
                     js_set(&patch, "action", "delete")?;
                     js_set(&patch, "obj", obj.to_string())?;
diff --git a/automerge-wasm/test/test.ts b/automerge-wasm/test/test.ts
index dd12a1537..6e5201ecd 100644
--- a/automerge-wasm/test/test.ts
+++ b/automerge-wasm/test/test.ts
@@ -956,7 +956,7 @@ describe('Automerge', () => {
         doc1.free()
     })
 
-    it.skip('should capture local increment ops', () => {
+    it('should capture local increment ops', () => {
         let doc1 = create('aaaa')
         doc1.enablePatches(true)
         doc1.put('_root', 'counter', 2, 'counter')
@@ -964,7 +964,7 @@ describe('Automerge', () => {
 
         assert.deepEqual(doc1.popPatches(), [
             {action: 'put', obj: '_root', key: 'counter', value: 2, datatype: 'counter', conflict: false},
-            {action: 'put', obj: '_root', key: 'counter', value: 6, datatype: 'counter', conflict: false},
+            {action: 'increment', obj: '_root', key: 'counter', value: 4},
         ])
         doc1.free()
     })
@@ -986,23 +986,41 @@ describe('Automerge', () => {
         doc1.free()
     })
 
-    it.skip('should support counters in a map', () => {
+    it('should support counters in a map', () => {
       let doc1 = create('aaaa'), doc2 = create('bbbb')
       doc2.enablePatches(true)
       doc1.put('_root', 'starlings', 2, 'counter')
       doc2.loadIncremental(doc1.saveIncremental())
       doc1.increment('_root', 'starlings', 1)
-      doc1.dump()
       doc2.loadIncremental(doc1.saveIncremental())
       assert.deepEqual(doc2.get('_root', 'starlings'), ['counter', 3])
       assert.deepEqual(doc2.popPatches(), [
         {action: 'put', obj: '_root', key: 'starlings', value: 2, datatype: 'counter', conflict: false},
-        {action: 'put', obj: '_root', key: 'starlings', value: 3, datatype: 'counter', conflict: false}
+        {action: 'increment', obj: '_root', key: 'starlings', value: 1}
       ])
       doc1.free(); doc2.free()
     })
 
-    it('should support counters in a list') // TODO
+    it('should support counters in a list', () => {
+      let doc1 = create('aaaa'), doc2 = create('bbbb')
+      doc2.enablePatches(true)
+      const list = doc1.putObject('_root', 'list', [])
+      doc2.loadIncremental(doc1.saveIncremental())
+      doc1.insert(list, 0, 1, 'counter')
+      doc2.loadIncremental(doc1.saveIncremental())
+      doc1.increment(list, 0, 2)
+      doc2.loadIncremental(doc1.saveIncremental())
+      doc1.increment(list, 0, -5)
+      doc2.loadIncremental(doc1.saveIncremental())
+
+      assert.deepEqual(doc2.popPatches(), [
+          {action: 'put', obj: '_root', key: 'list', value: list, datatype: 'list', conflict: false},
+          {action: 'insert', obj: list, key: 0, value: 1, datatype: 'counter'},
+          {action: 'increment', obj: list, key: 0, value: 2},
+          {action: 'increment', obj: list, key: 0, value: -5},
+      ])
+      doc1.free(); doc2.free()
+    })
 
     it('should delete a counter from a map') // TODO
   })
diff --git a/automerge/examples/watch.rs b/automerge/examples/watch.rs
index 4ba65e616..d96684970 100644
--- a/automerge/examples/watch.rs
+++ b/automerge/examples/watch.rs
@@ -66,6 +66,15 @@ fn get_changes(doc: &Automerge, patches: Vec<Patch>) {
                     doc.path_to_object(&obj)
                 )
             }
+            Patch::Increment { obj, key, value } => {
+                println!(
+                    "increment {:?} in obj {:?} by {:?}, object path {:?}",
+                    key,
+                    obj,
+                    value,
+                    doc.path_to_object(&obj)
+                )
+            }
             Patch::Delete { obj, key } => println!(
                 "delete {:?} in obj {:?}, object path {:?}",
                 key,
diff --git a/automerge/src/automerge.rs b/automerge/src/automerge.rs
index 534913cc1..d871ee415 100644
--- a/automerge/src/automerge.rs
+++ b/automerge/src/automerge.rs
@@ -1004,7 +1004,7 @@ impl Automerge {
 
     pub fn dump(&self) {
         log!(
-            "  {:12} {:12} {:12} {} {} {}",
+            "  {:12} {:12} {:12} {:12} {:12} {:12}",
             "id",
             "obj",
             "key",
@@ -1028,7 +1028,7 @@ impl Automerge {
             let pred: Vec<_> = op.pred.iter().map(|id| self.to_string(*id)).collect();
             let succ: Vec<_> = op.succ.iter().map(|id| self.to_string(*id)).collect();
             log!(
-                "  {:12} {:12} {:12} {} {:?} {:?}",
+                "  {:12} {:12} {:12} {:12} {:12?} {:12?}",
                 id,
                 obj,
                 key,
@@ -2005,4 +2005,96 @@ mod tests {
         let len = doc.length(&text);
         assert_eq!(len, 4); // 4 chars
     }
+
+    #[test]
+    fn observe_counter_change_application_overwrite() {
+        let mut doc1 = AutoCommit::new();
+        doc1.set_actor(ActorId::from([1]));
+        doc1.put(ROOT, "counter", ScalarValue::counter(1)).unwrap();
+        doc1.commit();
+
+        let mut doc2 = doc1.fork();
+        doc2.set_actor(ActorId::from([2]));
+        doc2.put(ROOT, "counter", "mystring").unwrap();
+        doc2.commit();
+
+        doc1.increment(ROOT, "counter", 2).unwrap();
+        doc1.commit();
+        doc1.increment(ROOT, "counter", 5).unwrap();
+        doc1.commit();
+
+        let mut observer = VecOpObserver::default();
+        let mut doc3 = doc1.clone();
+        doc3.merge_with(
+            &mut doc2,
+            ApplyOptions::default().with_op_observer(&mut observer),
+        )
+        .unwrap();
+
+        assert_eq!(
+            observer.take_patches(),
+            vec![Patch::Put {
+                obj: ExId::Root,
+                key: Prop::Map("counter".into()),
+                value: (
+                    ScalarValue::Str("mystring".into()).into(),
+                    ExId::Id(2, doc2.get_actor().clone(), 1)
+                ),
+                conflict: false
+            }]
+        );
+
+        let mut observer = VecOpObserver::default();
+        let mut doc4 = doc2.clone();
+        doc4.merge_with(
+            &mut doc1,
+            ApplyOptions::default().with_op_observer(&mut observer),
+        )
+        .unwrap();
+
+        // no patches as the increments operate on an invisible counter
+        assert_eq!(observer.take_patches(), vec![]);
+    }
+
+    #[test]
+    fn observe_counter_change_application() {
+        let mut doc = AutoCommit::new();
+        doc.put(ROOT, "counter", ScalarValue::counter(1)).unwrap();
+        doc.increment(ROOT, "counter", 2).unwrap();
+        doc.increment(ROOT, "counter", 5).unwrap();
+        let changes = doc.get_changes(&[]).into_iter().cloned().collect();
+
+        let mut new_doc = AutoCommit::new();
+        let mut observer = VecOpObserver::default();
+        new_doc
+            .apply_changes_with(
+                changes,
+                ApplyOptions::default().with_op_observer(&mut observer),
+            )
+            .unwrap();
+        assert_eq!(
+            observer.take_patches(),
+            vec![
+                Patch::Put {
+                    obj: ExId::Root,
+                    key: Prop::Map("counter".into()),
+                    value: (
+                        ScalarValue::counter(1).into(),
+                        ExId::Id(1, doc.get_actor().clone(), 0)
+                    ),
+                    conflict: false
+                },
+                Patch::Increment {
+                    obj: ExId::Root,
+                    key: Prop::Map("counter".into()),
+                    value: (2, ExId::Id(2, doc.get_actor().clone(), 0)),
+                },
+                Patch::Increment {
+                    obj: ExId::Root,
+                    key: Prop::Map("counter".into()),
+                    value: (5, ExId::Id(3, doc.get_actor().clone(), 0)),
+                }
+            ]
+        );
+    }
 }
diff --git a/automerge/src/op_observer.rs b/automerge/src/op_observer.rs
index 307188351..6a6652426 100644
--- a/automerge/src/op_observer.rs
+++ b/automerge/src/op_observer.rs
@@ -21,6 +21,14 @@ pub trait OpObserver {
     /// - `conflict`: whether this put conflicts with other operations.
     fn put(&mut self, objid: ExId, key: Prop, tagged_value: (Value, ExId), conflict: bool);
 
+    /// A counter has been incremented.
+    ///
+    /// - `objid`: the object that contains the counter.
+    /// - `key`: they key that the chounter is at.
+    /// - `tagged_value`: the amount the counter has been incremented by, and the the id of the
+    /// increment operation.
+    fn increment(&mut self, objid: ExId, key: Prop, tagged_value: (i64, ExId));
+
     /// A value has beeen deleted.
     ///
     /// - `objid`: the object that has been deleted in.
@@ -33,6 +41,8 @@ impl OpObserver for () {
 
     fn put(&mut self, _objid: ExId, _key: Prop, _tagged_value: (Value, ExId), _conflict: bool) {}
 
+    fn increment(&mut self, _objid: ExId, _key: Prop, _tagged_value: (i64, ExId)) {}
+
     fn delete(&mut self, _objid: ExId, _key: Prop) {}
 }
 
@@ -68,6 +78,14 @@ impl OpObserver for VecOpObserver {
         });
     }
 
+    fn increment(&mut self, objid: ExId, key: Prop, tagged_value: (i64, ExId)) {
+        self.patches.push(Patch::Increment {
+            obj: objid,
+            key,
+            value: tagged_value,
+        });
+    }
+
     fn delete(&mut self, objid: ExId, key: Prop) {
         self.patches.push(Patch::Delete { obj: objid, key })
     }
@@ -96,6 +114,16 @@ pub enum Patch {
         /// The value that was inserted, and the id of the operation that inserted it there.
         value: (Value<'static>, ExId),
     },
+    /// Incrementing a counter.
+    Increment {
+        /// The object that was incremented in.
+        obj: ExId,
+        /// The key that was incremented.
+        key: Prop,
+        /// The amount that the counter was incremented by, and the id of the operation that
+        /// did the increment.
+        value: (i64, ExId),
+    },
     /// Deleting an element from a list/text
     Delete {
         /// The object that was deleted from.
diff --git a/automerge/src/op_set.rs b/automerge/src/op_set.rs
index 022750ca1..f16822da5 100644
--- a/automerge/src/op_set.rs
+++ b/automerge/src/op_set.rs
@@ -202,6 +202,13 @@ impl OpSetInternal {
             } else {
                 observer.delete(ex_obj, key);
             }
+        } else if let Some(value) = op.get_increment_value() {
+            // only observe this increment if the counter is visible, i.e. the counter's
+            // create op is in the values
+            if values.iter().any(|value| op.pred.contains(&value.id)) {
+                // we have observed the value
+                observer.increment(ex_obj, key, (value, self.id_to_exid(op.id)));
+            }
         } else {
             let winner = if let Some(last_value) = values.last() {
                 if self.m.lamport_cmp(op.id, last_value.id) == Ordering::Greater {
diff --git a/automerge/src/query/seek_op_with_patch.rs b/automerge/src/query/seek_op_with_patch.rs
index d25d8dcc4..fab58a0d7 100644
--- a/automerge/src/query/seek_op_with_patch.rs
+++ b/automerge/src/query/seek_op_with_patch.rs
@@ -135,6 +135,11 @@ impl<'a> TreeQuery<'a> for SeekOpWithPatch<'a> {
 
                     // Keep track of any ops we're overwriting and any conflicts on this key
                     if self.op.overwrites(op) {
+                        // when we encounter an increment op we also want to find the counter for
+                        // it.
+                        if self.op.is_inc() && op.is_counter() && op.visible() {
+                            self.values.push(op);
+                        }
                         self.succ.push(self.pos);
                     } else if op.visible() {
                         self.values.push(op);
@@ -145,6 +150,7 @@ impl<'a> TreeQuery<'a> for SeekOpWithPatch<'a> {
                     if m.lamport_cmp(op.id, self.op.id) == Ordering::Greater {
                         break;
                     }
+
                     self.pos += 1;
                 }
 
@@ -178,6 +184,11 @@ impl<'a> TreeQuery<'a> for SeekOpWithPatch<'a> {
             if self.is_target_insert(e) {
                 self.found = true;
                 if self.op.overwrites(e) {
+                    // when we encounter an increment op we also want to find the counter for
+                    // it.
+                    if self.op.is_inc() && e.is_counter() && e.visible() {
+                        self.values.push(e);
+                    }
                     self.succ.push(self.pos);
                 }
                 if e.visible() {
@@ -190,6 +201,11 @@ impl<'a> TreeQuery<'a> for SeekOpWithPatch<'a> {
             // Once we've found the reference element, keep track of any ops that we're overwriting
             let overwritten = self.op.overwrites(e);
             if overwritten {
+                // when we encounter an increment op we also want to find the counter for
+                // it.
+                if self.op.is_inc() && e.is_counter() && e.visible() {
+                    self.values.push(e);
+                }
                 self.succ.push(self.pos);
             }
 
diff --git a/automerge/src/transaction/inner.rs b/automerge/src/transaction/inner.rs
index 4b4ad60dc..4f291da90 100644
--- a/automerge/src/transaction/inner.rs
+++ b/automerge/src/transaction/inner.rs
@@ -53,6 +53,8 @@ impl TransactionInner {
                     }
                 } else if op.is_delete() {
                     observer.delete(ex_obj, prop.clone());
+                } else if let Some(value) = op.get_increment_value() {
+                    observer.increment(ex_obj, prop.clone(), (value, doc.id_to_exid(op.id)));
                 } else {
                     let value = (op.value(), doc.ops.id_to_exid(op.id));
                     observer.put(ex_obj, prop.clone(), value, false);
diff --git a/automerge/src/types.rs b/automerge/src/types.rs
index 26b4f3ce3..ee5adf013 100644
--- a/automerge/src/types.rs
+++ b/automerge/src/types.rs
@@ -459,6 +459,14 @@ impl Op {
         }
     }
 
+    pub fn get_increment_value(&self) -> Option<i64> {
+        if let OpType::Increment(i) = self.action {
+            Some(i)
+        } else {
+            None
+        }
+    }
+
     pub fn value(&self) -> Value {
         match &self.action {
             OpType::Make(obj_type) => Value::Object(*obj_type),
diff --git a/automerge/tests/test.rs b/automerge/tests/test.rs
index 2bc46b745..d837a59d8 100644
--- a/automerge/tests/test.rs
+++ b/automerge/tests/test.rs
@@ -1,6 +1,6 @@
 use automerge::transaction::Transactable;
 use automerge::{
-    ActorId, AutoCommit, Automerge, AutomergeError, ObjType, ScalarValue, Value, ROOT,
+    ActorId, ApplyOptions, AutoCommit, Automerge, AutomergeError, ObjType, ScalarValue, Value, VecOpObserver, ROOT,
 };
 
 mod helpers;
@@ -930,6 +930,23 @@ fn list_counter_del() -> Result<(), automerge::AutomergeError> {
     Ok(())
 }
 
+#[test]
+fn observe_counter_change_application() {
+    let mut doc = AutoCommit::new();
+    doc.put(ROOT, "counter", ScalarValue::counter(1)).unwrap();
+    doc.increment(ROOT, "counter", 2).unwrap();
+    doc.increment(ROOT, "counter", 5).unwrap();
+    let changes = doc.get_changes(&[]).into_iter().cloned().collect();
+
+    let mut doc = AutoCommit::new();
+    let mut observer = VecOpObserver::default();
+    doc.apply_changes_with(
+        changes,
+        ApplyOptions::default().with_op_observer(&mut observer),
+    )
+    .unwrap();
+}
+
 #[test]
 fn increment_non_counter_map() {
     let mut doc = AutoCommit::new();