diff --git a/chaco/axis.py b/chaco/axis.py
index 503f150e8..e7ca1ed7c 100644
--- a/chaco/axis.py
+++ b/chaco/axis.py
@@ -607,12 +607,12 @@ def _bounds_items_changed(self, event):
 
     def _mapper_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self.mapper_updated, "updated", remove=True)
+            old.observe(self.mapper_updated, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self.mapper_updated, "updated")
+            new.observe(self.mapper_updated, "updated")
         self._invalidate()
 
-    def mapper_updated(self):
+    def mapper_updated(self, event=None):
         """
         Event handler that is bound to this axis's mapper's **updated** event
         """
diff --git a/chaco/barplot.py b/chaco/barplot.py
index 680a60b3a..c32b9fad4 100644
--- a/chaco/barplot.py
+++ b/chaco/barplot.py
@@ -423,10 +423,10 @@ def _orientation_changed(self):
 
     def _index_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._either_data_changed, "data_changed", remove=True)
+            old.observe(self._either_data_updated, "data_changed", remove=True)
         if new is not None:
-            new.on_trait_change(self._either_data_changed, "data_changed")
-        self._either_data_changed()
+            new.observe(self._either_data_updated, "data_changed")
+        self._either_data_updated()
 
     def _index_direction_changed(self):
         m = self.index_mapper
@@ -438,17 +438,17 @@ def _value_direction_changed(self):
         m.low_pos, m.high_pos = m.high_pos, m.low_pos
         self.invalidate_draw()
 
-    def _either_data_changed(self):
+    def _either_data_updated(self, event=None):
         self.invalidate_draw()
         self._cache_valid = False
         self.request_redraw()
 
     def _value_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._either_data_changed, "data_changed", remove=True)
+            old.observe(self._either_data_updated, "data_changed", remove=True)
         if new is not None:
-            new.on_trait_change(self._either_data_changed, "data_changed")
-        self._either_data_changed()
+            new.observe(self._either_data_updated, "data_changed")
+        self._either_data_updated()
 
     def _index_mapper_changed(self, old, new):
         return self._either_mapper_changed(old, new)
@@ -458,12 +458,12 @@ def _value_mapper_changed(self, old, new):
 
     def _either_mapper_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._mapper_updated_handler, "updated", remove=True)
+            old.observe(self._mapper_updated_handler, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self._mapper_updated_handler, "updated")
+            new.observe(self._mapper_updated_handler, "updated")
         self.invalidate_draw()
 
-    def _mapper_updated_handler(self):
+    def _mapper_updated_handler(self, event):
         self._cache_valid = False
         self.invalidate_draw()
         self.request_redraw()
diff --git a/chaco/base_1d_mapper.py b/chaco/base_1d_mapper.py
index 25a3a5444..88b639ef1 100644
--- a/chaco/base_1d_mapper.py
+++ b/chaco/base_1d_mapper.py
@@ -64,18 +64,17 @@ def _high_pos_changed(self, old, new):
 
     def _range_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._range_change_handler, "updated",
-                                remove = True)
+            old.observe(self._range_change_handler, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self._range_change_handler, "updated")
+            new.observe(self._range_change_handler, "updated")
 
         self._cache_valid = False
         self.updated = new
 
-    def _range_change_handler(self, obj, name, new):
+    def _range_change_handler(self, event):
         "Handles the range changing; dynamically attached to our ranges"
         self._cache_valid = False
-        self.updated = obj
+        self.updated = event.object
 
     def _get_screen_bounds(self):
         return (self.low_pos, self.high_pos)
diff --git a/chaco/base_2d_plot.py b/chaco/base_2d_plot.py
index 1dca340ae..e12b9dab6 100644
--- a/chaco/base_2d_plot.py
+++ b/chaco/base_2d_plot.py
@@ -89,14 +89,11 @@ def __init__(self, **kwargs):
         self.trait_set(**kwargs_tmp)
         super(Base2DPlot, self).__init__(**kwargs)
         if self.index is not None:
-            self.index.on_trait_change(self._update_index_data,
-                                       "data_changed")
+            self.index.observe(self._update_index_data, "data_changed")
         if self.index_mapper:
-            self.index_mapper.on_trait_change(self._update_index_mapper,
-                                              "updated")
+            self.index_mapper.observe(self._update_index_mapper, "updated")
         if self.value is not None:
-            self.value.on_trait_change(self._update_value_data,
-                                       "data_changed")
+            self.value.observe(self._update_value_data, "data_changed")
         # If we are not resizable, we will not get a bounds update upon layout,
         # so we have to manually update our mappers
         if self.resizable == "":
@@ -245,7 +242,7 @@ def _get_y_mapper(self):
     # Private methods
     #------------------------------------------------------------------------
 
-    def _update_index_mapper(self):
+    def _update_index_mapper(self, event=None):
         """ Updates the index mapper.
 
         Called by various trait change handlers.
@@ -278,7 +275,7 @@ def _update_index_mapper(self):
             self.index_mapper_changed = True
             self.invalidate_draw()
 
-    def _update_index_data(self):
+    def _update_index_data(self, event=None):
         """ Updates the index data.
 
         Called by various trait change handlers.
@@ -286,7 +283,7 @@ def _update_index_data(self):
         self.index_data_changed = True
         self.invalidate_draw()
 
-    def _update_value_data(self):
+    def _update_value_data(self, event=None):
         """ Updates the value data.
 
         Called by various trait change handlers.
@@ -315,25 +312,21 @@ def _origin_changed(self):
 
     def _index_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._update_index_data,
-                                "data_changed", remove=True)
+            old.obseve(self._update_index_data, "data_changed", remove=True)
         if new is not None:
-            new.on_trait_change(self._update_index_data, "data_changed")
+            new.obseve(self._update_index_data, "data_changed")
         self._update_index_data()
 
     def _value_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._update_value_data,
-                                "data_changed", remove=True)
+            old.observe(self._update_value_data, "data_changed", remove=True)
         if new is not None:
-            new.on_trait_change(self._update_value_data, "data_changed")
+            new.observe(self._update_value_data, "data_changed")
         self._update_value_data()
 
     def _index_mapper_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._update_index_mapper,
-                                "updated", remove=True)
+            old.observe(self._update_index_mapper, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self._update_index_mapper, "updated")
+            new.observe(self._update_index_mapper, "updated")
         self._update_index_mapper()
-
diff --git a/chaco/base_contour_plot.py b/chaco/base_contour_plot.py
index 3520a6a4c..22d384e85 100644
--- a/chaco/base_contour_plot.py
+++ b/chaco/base_contour_plot.py
@@ -65,7 +65,7 @@ class BaseContourPlot(Base2DPlot):
     def __init__(self, *args, **kwargs):
         super(BaseContourPlot, self).__init__(*args, **kwargs)
         if self.color_mapper:
-            self.color_mapper.on_trait_change(self._update_color_mapper, "updated")
+            self.color_mapper.observe(self._update_color_mapper, "updated")
 
     def _update_levels(self):
         """ Updates the levels cache.  """
@@ -149,7 +149,7 @@ def _index_mapper_changed_fired(self):
         # If the index mapper has changed, then we need to redraw
         self.invalidate_and_redraw()
 
-    def _update_color_mapper(self):
+    def _update_color_mapper(self, event=None):
         # If the color mapper has changed, then we need to recompute the
         # levels and cached data associated with that.
         self._level_cache_valid = False
@@ -177,7 +177,7 @@ def _get_color_mapper(self):
     def _set_color_mapper(self, color_mapper):
         # Remove the dynamic event handler from the old color mapper
         if self.colors is not None and isinstance(self.colors, ColorMapper):
-            self.colors.on_trait_change(self._update_color_mapper, "updated", remove=True)
+            self.colors.observe(self._update_color_mapper, "updated", remove=True)
 
             # Check to see if we should copy over the range as well
             if color_mapper is not None:
@@ -186,7 +186,7 @@ def _set_color_mapper(self, color_mapper):
 
         # Attach the dynamic event handler to the new color mapper
         if color_mapper is not None:
-            color_mapper.on_trait_change(self._update_color_mapper, "updated")
+            color_mapper.observe(self._update_color_mapper, "updated")
 
         self.colors = color_mapper
         self._update_color_mapper()
diff --git a/chaco/base_xy_plot.py b/chaco/base_xy_plot.py
index 96e8daf01..2f5fdb0df 100644
--- a/chaco/base_xy_plot.py
+++ b/chaco/base_xy_plot.py
@@ -183,15 +183,15 @@ def __init__(self, **kwtraits):
         self.trait_set(**kwargs_tmp)
         AbstractPlotRenderer.__init__(self, **kwtraits)
         if self.index is not None:
-            self.index.on_trait_change(self._either_data_changed, "data_changed")
-            self.index.on_trait_change(self._either_metadata_changed, "metadata_changed")
+            self.index.observe(self._either_data_updated, "data_changed")
+            self.index.observe(self._either_metadata_updated, "metadata_changed")
         if self.index_mapper:
-            self.index_mapper.on_trait_change(self._mapper_updated_handler, "updated")
+            self.index_mapper.observe(self._mapper_updated_handler, "updated")
         if self.value is not None:
-            self.value.on_trait_change(self._either_data_changed, "data_changed")
-            self.value.on_trait_change(self._either_metadata_changed, "metadata_changed")
+            self.value.observe(self._either_data_updated, "data_changed")
+            self.value.observe(self._either_metadata_updated, "metadata_changed")
         if self.value_mapper:
-            self.value_mapper.on_trait_change(self._mapper_updated_handler, "updated")
+            self.value_mapper.observe(self._mapper_updated_handler, "updated")
 
         # If we are not resizable, we will not get a bounds update upon layout,
         # so we have to manually update our mappers
@@ -614,33 +614,33 @@ def _orientation_changed(self):
 
     def _index_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._either_data_changed, "data_changed", remove=True)
-            old.on_trait_change(self._either_metadata_changed, "metadata_changed",
-                                remove=True)
+            old.observe(self._either_data_updated, "data_changed", remove=True)
+            old.observe(self._either_metadata_updated, "metadata_changed",
+                        remove=True)
         if new is not None:
-            new.on_trait_change(self._either_data_changed, "data_changed")
-            new.on_trait_change(self._either_metadata_changed, "metadata_changed")
-        self._either_data_changed()
+            new.observe(self._either_data_updated, "data_changed")
+            new.observe(self._either_metadata_updated, "metadata_changed")
+        self._either_data_updated()
 
-    def _either_data_changed(self):
+    def _either_data_updated(self, event=None):
         self.invalidate_draw()
         self._cache_valid = False
         self._screen_cache_valid = False
         self.request_redraw()
 
-    def _either_metadata_changed(self):
+    def _either_metadata_updated(self, event):
         # By default, don't respond to metadata change events.
         pass
 
     def _value_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._either_data_changed, "data_changed", remove=True)
-            old.on_trait_change(self._either_metadata_changed, "metadata_changed",
-                                remove=True)
+            old.observe(self._either_data_updated, "data_changed", remove=True)
+            old.observe(self._either_metadata_updated, "metadata_changed",
+                        remove=True)
         if new is not None:
-            new.on_trait_change(self._either_data_changed, "data_changed")
-            new.on_trait_change(self._either_metadata_changed, "metadata_changed")
-        self._either_data_changed()
+            new.observe(self._either_data_updated, "data_changed")
+            new.observe(self._either_metadata_updated, "metadata_changed")
+        self._either_data_updated()
 
     def _origin_changed(self, old, new):
         # origin switch from left to right or vice versa?
@@ -671,13 +671,13 @@ def _value_mapper_changed(self, old, new):
 
     def _either_mapper_changed(self, obj, name, old, new):
         if old is not None:
-            old.on_trait_change(self._mapper_updated_handler, "updated", remove=True)
+            old.observe(self._mapper_updated_handler, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self._mapper_updated_handler, "updated")
+            new.observe(self._mapper_updated_handler, "updated")
         self.invalidate_draw()
         self._screen_cache_valid = False
 
-    def _mapper_updated_handler(self):
+    def _mapper_updated_handler(self, event):
         self._cache_valid = False
         self._screen_cache_valid = False
         self.invalidate_draw()
@@ -710,9 +710,9 @@ def __getstate__(self):
     def __setstate__(self, state):
         super(BaseXYPlot, self).__setstate__(state)
         if self.index is not None:
-            self.index.on_trait_change(self._either_data_changed, "data_changed")
+            self.index.observe(self._either_data_updated, "data_changed")
         if self.value is not None:
-            self.value.on_trait_change(self._either_data_changed, "data_changed")
+            self.value.observe(self._either_data_updated, "data_changed")
 
         self.invalidate_draw()
         self._cache_valid = False
diff --git a/chaco/chaco_plot_editor.py b/chaco/chaco_plot_editor.py
index 630fa260d..8c5922cc5 100644
--- a/chaco/chaco_plot_editor.py
+++ b/chaco/chaco_plot_editor.py
@@ -243,11 +243,11 @@ def init ( self, parent ):
         object = self.object
         if USE_DATA_UPDATE == 1:
             for name in (plotitem.index, plotitem.value):
-                object.on_trait_change( self._update_data, name)
+                object.observe( self._update_data, name)
         for name in (plotitem.x_label_trait, plotitem.y_label_trait):
-            object.on_trait_change(lambda s: self._update_axis_grids(), name)
+            object.observe(lambda s: self._update_axis_grids(), name)
         if plotitem.type_trait not in ("", None):
-            object.on_trait_change(self.update_editor, plotitem.type_trait)
+            object.observe(self.update_editor, plotitem.type_trait)
 
     #---------------------------------------------------------------------------
     #  Disposes of the contents of an editor:
@@ -261,9 +261,9 @@ def dispose(self):
 
         if USE_DATA_UPDATE == 1:
             for name in (plotitem.index, plotitem.value):
-                object.on_trait_change( self._update_data, name, remove = True )
+                object.observe( self._update_data, name, remove = True )
         for name in (plotitem.type_trait,):
-            object.on_trait_change( self.update_editor, name, remove = True )
+            object.observe( self.update_editor, name, remove = True )
         self._destroy_plot()
         super(ChacoPlotEditor, self).dispose()
 
@@ -283,7 +283,7 @@ def _destroy_plot(self):
     #  Updates the editor when the object trait changes externally to the editor:
     #---------------------------------------------------------------------------
 
-    def update_editor(self):
+    def update_editor(self, event=None):
         """ Updates the editor when the object trait changes externally to the
             editor.
         """
@@ -340,7 +340,7 @@ def update_editor(self):
         self._container.add(plot)
         self._container.request_redraw()
 
-    def _update_data(self):
+    def _update_data(self, event):
         """ Updates the editor when the object trait changes externally to the
             editor.
         """
diff --git a/chaco/cmap_image_plot.py b/chaco/cmap_image_plot.py
index 37aa35821..46cd9d531 100644
--- a/chaco/cmap_image_plot.py
+++ b/chaco/cmap_image_plot.py
@@ -64,11 +64,9 @@ class CMapImagePlot(ImagePlot):
     def __init__(self, **kwargs):
         super(CMapImagePlot, self).__init__(**kwargs)
         if self.value_mapper:
-            self.value_mapper.on_trait_change(self._update_value_mapper,
-                                              "updated")
+            self.value_mapper.observe(self._update_value_mapper, "updated")
         if self.value:
-            self.value.on_trait_change(self._update_selections,
-                                       "metadata_changed")
+            self.value.observe(self._update_selections, "metadata_changed")
 
     def set_value_selection(self, val):
         """ Sets a range of values in the value data source as selected.
@@ -139,12 +137,12 @@ def _compute_cached_image(self, selection_masks=None):
             ImagePlot._compute_cached_image(self, self.value.data, mapper=lambda data:
                 self._cmap_values(data))
             
-    def _update_value_mapper(self):
+    def _update_value_mapper(self, event=None):
         self._mapped_image_cache_valid = False
         self._image_cache_valid = False
         self.invalidate_and_redraw()
 
-    def _update_selections(self):
+    def _update_selections(self, event=None):
         self._mapped_image_cache_valid = False
         self._image_cache_valid = False
         self.invalidate_and_redraw()
@@ -171,10 +169,9 @@ def _set_color_mapper(self, val):
 
     def _value_mapper_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._update_value_mapper,
-                                "updated", remove=True)
+            old.observe(self._update_value_mapper, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self._update_value_mapper, "updated")
+            new.observe(self._update_value_mapper, "updated")
 
         if old and new:
             if new.range is None and old.range is not None:
@@ -192,4 +189,3 @@ def _index_data_changed_fired(self):
     def _cache_full_map_changed(self):
         self._mapped_image_cache_valid = False
         
-
diff --git a/chaco/color_mapper.py b/chaco/color_mapper.py
index 50b3339e0..b094e5fdb 100644
--- a/chaco/color_mapper.py
+++ b/chaco/color_mapper.py
@@ -424,13 +424,12 @@ def _map(self, X):
 
     def _range_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._range_change_handler, "updated",
-                                remove = True)
+            old.observe(self._range_change_handler, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self._range_change_handler, "updated")
+            new.observe(self._range_change_handler, "updated")
 
         self.updated = new
 
-    def _range_change_handler(self, obj, name, new):
+    def _range_change_handler(self, event):
         "Handles the range changing; dynamically attached to our ranges"
-        self.updated = obj
+        self.updated = event.object
diff --git a/chaco/colormapped_scatterplot.py b/chaco/colormapped_scatterplot.py
index d5372b076..acf7f5ae4 100644
--- a/chaco/colormapped_scatterplot.py
+++ b/chaco/colormapped_scatterplot.py
@@ -384,10 +384,10 @@ def draw_func(x, y, size):
 
     def _color_data_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._either_data_changed, "data_changed", remove=True)
+            old.observe(self._either_data_updated, "data_changed", remove=True)
         if new is not None:
-            new.on_trait_change(self._either_data_changed, "data_changed")
-        self._either_data_changed()
+            new.observe(self._either_data_updated, "data_changed")
+        self._either_data_updated()
 
     def _color_mapper_changed(self, old, new):
         self._cache_valid = False
diff --git a/chaco/colormapped_selection_overlay.py b/chaco/colormapped_selection_overlay.py
index 8e057b48a..718cb205f 100644
--- a/chaco/colormapped_selection_overlay.py
+++ b/chaco/colormapped_selection_overlay.py
@@ -6,6 +6,7 @@
 
 # Enthought library imports
 from traits.api import Any, Bool, Float, Instance, Property, Enum
+from traits.observation.events import TraitChangeEvent
 
 # Local imports
 from .abstract_overlay import AbstractOverlay
@@ -100,22 +101,41 @@ def overlay(self, component, gc, view_bounds=None, mode="normal"):
 
     def _component_changed(self, old, new):
         if old:
-            old.on_trait_change(self.datasource_change_handler, "color_data", remove=True)
+            old.observe(self.datasource_change_handler, "color_data", remove=True)
         if new:
-            new.on_trait_change(self.datasource_change_handler, "color_data")
+            new.observe(self.datasource_change_handler, "color_data")
             self._old_alpha = new.fill_alpha
             self._old_outline_color = new.outline_color
             self._old_line_width = new.line_width
-            self.datasource_change_handler(new, "color_data", None, new.color_data)
+            
+            self.datasource_change_handler(
+                TraitChangeEvent(
+                    object=new,
+                    name="color_data",
+                    old=None,
+                    new=new.color_data
+                )
+            )
+
+    def datasource_change_handler(self, event):
+        obj, name, old, new = (event.object, event.name, event.old, event.new)
 
-    def datasource_change_handler(self, obj, name, old, new):
         if old:
-            old.on_trait_change(self.selection_change_handler, "metadata_changed", remove=True)
+            old.observe(self.selection_change_handler, "metadata_changed", remove=True)
         if new:
-            new.on_trait_change(self.selection_change_handler, "metadata_changed")
-            self.selection_change_handler(new, "metadata_changed", None, new.metadata)
+            new.observe(self.selection_change_handler, "metadata_changed")
+            self.selection_change_handler(
+                TraitChangeEvent(
+                    object=new,
+                    name="metadata_changed",
+                    old=None,
+                    new=new.metadata
+                )
+            )
+
+    def selection_change_handler(self, event):
+        obj, name, old, new = (event.object, event.name, event.old, event.new)
 
-    def selection_change_handler(self, obj, name, old, new):
         if self.selection_type == 'range':
             selection_key = 'selections'
         elif self.selection_type == 'mask':
diff --git a/chaco/data_label.py b/chaco/data_label.py
index 79d36103d..b9b76b9c9 100644
--- a/chaco/data_label.py
+++ b/chaco/data_label.py
@@ -533,10 +533,9 @@ def _component_changed(self, old, new):
 
     def _modify_mapper_listeners(self, mapper, attach=True):
         if mapper is not None:
-            mapper.on_trait_change(self._handle_mapper, 'updated',
-                                   remove=not attach)
+            mapper.observe(self._handle_mapper, 'updated', remove=not attach)
 
-    def _handle_mapper(self):
+    def _handle_mapper(self, event):
         # This gets fired whenever a mapper on our plot fires its
         # 'updated' event.
         self._layout_needed = True
diff --git a/chaco/data_range_1d.py b/chaco/data_range_1d.py
index 85fee63c0..cfd9f70b0 100644
--- a/chaco/data_range_1d.py
+++ b/chaco/data_range_1d.py
@@ -189,7 +189,7 @@ def reset(self):
         self._refresh_bounds()
         self.tracking_amount = self.default_tracking_amount
 
-    def refresh(self):
+    def refresh(self, event=None):
         """ If any of the bounds is 'auto', this method refreshes the actual
         low and high values from the set of the view filters' data sources.
         """
@@ -372,16 +372,16 @@ def _do_track(self):
     def _sources_items_changed(self, event):
         self.refresh()
         for source in event.removed:
-            source.on_trait_change(self.refresh, "data_changed", remove=True)
+            source.observe(self.refresh, "data_changed", remove=True)
         for source in event.added:
-            source.on_trait_change(self.refresh, "data_changed")
+            source.observe(self.refresh, "data_changed")
 
     def _sources_changed(self, old, new):
         self.refresh()
         for source in old:
-            source.on_trait_change(self.refresh, "data_changed", remove=True)
+            source.observe(self.refresh, "data_changed", remove=True)
         for source in new:
-            source.on_trait_change(self.refresh, "data_changed")
+            source.observe(self.refresh, "data_changed")
 
     #------------------------------------------------------------------------
     # Serialization interface
diff --git a/chaco/data_range_2d.py b/chaco/data_range_2d.py
index 37ce223d6..97ad908ad 100644
--- a/chaco/data_range_2d.py
+++ b/chaco/data_range_2d.py
@@ -117,7 +117,7 @@ def reset(self):
         self.low_setting = ('auto', 'auto')
         self.refresh()
 
-    def refresh(self):
+    def refresh(self, event=None):
         """ If any of the bounds is 'auto', this method refreshes the actual
         low and high values from the set of the view filters' data sources.
         """
@@ -204,9 +204,9 @@ def _set_1d_range(self, dataname, oldrange, newrange):
 
     def _sources_items_changed(self, event):
         for source in event.removed:
-            source.on_trait_change(self.refresh, "data_changed", remove=True)
+            source.observe(self.refresh, "data_changed", remove=True)
         for source in event.added:
-            source.on_trait_change(self.refresh, "data_changed")
+            source.observe(self.refresh, "data_changed")
         # the _xdata and _ydata of the sources may be created anew on every
         # access, so we can't just add/delete from _xrange and _yrange sources
         # based on object identity. So recreate lists each time:
@@ -216,9 +216,9 @@ def _sources_items_changed(self, event):
 
     def _sources_changed(self, old, new):
         for source in old:
-            source.on_trait_change(self.refresh, "data_changed", remove=True)
+            source.observe(self.refresh, "data_changed", remove=True)
         for source in new:
-            source.on_trait_change(self.refresh, "data_changed")
+            source.observe(self.refresh, "data_changed")
         # the _xdata and _ydata of the sources may be created anew on every
         # access, so we can't just add/delete from _xrange and _yrange sources
         # based on object identity. So recreate lists each time:
diff --git a/chaco/grid.py b/chaco/grid.py
index 0025e481d..f909cb694 100644
--- a/chaco/grid.py
+++ b/chaco/grid.py
@@ -345,12 +345,12 @@ def _draw_component(self, gc, view_bounds=None, mode="normal"):
 
     def _mapper_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self.mapper_updated, "updated", remove=True)
+            old.observe(self.mapper_updated, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self.mapper_updated, "updated")
+            new.observe(self.mapper_updated, "updated")
         self.invalidate()
 
-    def mapper_updated(self):
+    def mapper_updated(self, event=None):
         """
         Event handler that is bound to this mapper's **updated** event.
         """
diff --git a/chaco/grid_mapper.py b/chaco/grid_mapper.py
index 1519c9c5e..907d2e8ab 100644
--- a/chaco/grid_mapper.py
+++ b/chaco/grid_mapper.py
@@ -146,7 +146,7 @@ def _update_bounds(self):
             self._ymapper.screen_bounds = (self.y_low_pos, self.y_high_pos)
         self.updated = True
 
-    def _update_range(self):
+    def _update_range(self, event=None):
         self.updated = True
 
     def _update_aspect_x(self):
@@ -185,9 +185,9 @@ def _update_aspect_y(self):
 
     def _range_changed(self, old, new):
         if old is not None:
-            old.on_trait_change(self._update_range, "updated", remove=True)
+            old.observe(self._update_range, "updated", remove=True)
         if new is not None:
-            new.on_trait_change(self._update_range, "updated")
+            new.observe(self._update_range, "updated")
             if self._xmapper is not None:
                 self._xmapper.range = new.x_range
             if self._ymapper is not None:
diff --git a/chaco/overlays/databox.py b/chaco/overlays/databox.py
index a279d1aa6..b7707fcff 100644
--- a/chaco/overlays/databox.py
+++ b/chaco/overlays/databox.py
@@ -58,16 +58,14 @@ class DataBox(AbstractOverlay):
     def __init__(self, *args, **kw):
         super(DataBox, self).__init__(*args, **kw)
         if hasattr(self.component, "range2d"):
-            self.component.range2d._xrange.on_trait_change(self.my_component_moved, "updated")
-            self.component.range2d._yrange.on_trait_change(self.my_component_moved, "updated")
+            self.component.range2d._xrange.observe(self.my_component_moved, "updated")
+            self.component.range2d._yrange.observe(self.my_component_moved, "updated")
         elif hasattr(self.component, "x_mapper") and hasattr(self.component, "y_mapper"):
-            self.component.x_mapper.range.on_trait_change(self.my_component_moved, "updated")
-            self.component.y_mapper.range.on_trait_change(self.my_component_moved, "updated")
+            self.component.x_mapper.range.observe(self.my_component_moved, "updated")
+            self.component.y_mapper.range.observe(self.my_component_moved, "updated")
         else:
             raise RuntimeError("DataBox cannot find a suitable mapper on its component.")
-        self.component.on_trait_change(self.my_component_resized, "bounds")
-        self.component.on_trait_change(self.my_component_resized, "bounds_items")
-
+        self.component.observe(self.my_component_resized, "bounds.items")
 
     def overlay(self, component, gc, view_bounds=None, mode="normal"):
         if not self._position_valid:
@@ -154,7 +152,7 @@ def _update_bounds(self, event=None):
         self._data_bounds = [data_x2 - data_pos[0], data_y2 - data_pos[1]]
         self.trait_property_changed("data_bounds", self._data_bounds)
 
-    def my_component_moved(self):
+    def my_component_moved(self, event=None):
         if self.affinity == "screen":
             # If we have screen affinity, then we need to take our current position
             # and map that back down into data coords
@@ -163,9 +161,8 @@ def my_component_moved(self):
         self._bounds_valid = False
         self._position_valid = False
 
-    def my_component_resized(self):
+    def my_component_resized(self, event=None):
         self._bounds_valid = False
         self._position_valid = False
 
 
-
diff --git a/chaco/overlays/simple_inspector_overlay.py b/chaco/overlays/simple_inspector_overlay.py
index 5ee6844bc..a0e7acd9f 100644
--- a/chaco/overlays/simple_inspector_overlay.py
+++ b/chaco/overlays/simple_inspector_overlay.py
@@ -155,7 +155,8 @@ def _field_formatters_default(self):
         return [[basic_formatter('x', 2)], [basic_formatter('y', 2)]]
 
     def _new_value_updated(self, event):
-        if event is None:
+        new_value_event = event.new
+        if new_value_event is None:
             self.text_grid = array()
             if self.visibility == "auto":
                 self.visibility = False
@@ -165,7 +166,7 @@ def _new_value_updated(self, event):
         if self.tooltip_mode:
             self.alternate_position = self.inspector.last_mouse_position
 
-        d = event
+        d = new_value_event
         text = []
         self.text_grid.string_array = array([[formatter(**d) for formatter in row]
             for row in self.field_formatters])
@@ -178,14 +179,14 @@ def _visible_changed(self):
 
     def _inspector_changed(self, old, new):
         if old:
-            old.on_trait_event(self._new_value_updated, 'new_value', remove=True)
-            old.on_trait_change(self._tool_visible_changed, "visible", remove=True)
+            old.observe(self._new_value_updated, 'new_value', remove=True)
+            old.observe(self._tool_visible_changed, "visible", remove=True)
         if new:
-            new.on_trait_event(self._new_value_updated, 'new_value')
-            new.on_trait_change(self._tool_visible_changed, "visible")
+            new.observe(self._new_value_updated, 'new_value')
+            new.observe(self._tool_visible_changed, "visible")
             self._tool_visible_changed()
 
-    def _tool_visible_changed(self):
+    def _tool_visible_changed(self, event=None):
         self.visibility = self.inspector.visible
         if self.visibility != "auto":
             self.visible = self.visibility
diff --git a/chaco/plot.py b/chaco/plot.py
index 68af267af..f1d369642 100644
--- a/chaco/plot.py
+++ b/chaco/plot.py
@@ -1238,24 +1238,25 @@ def _color_mapper_changed(self):
 
     def _data_changed(self, old, new):
         if old:
-            old.on_trait_change(self._data_update_handler, "data_changed",
-                                remove=True)
+            old.observe(self._data_update_handler, "data_changed", remove=True)
         if new:
-            new.on_trait_change(self._data_update_handler, "data_changed")
+            new.observe(self._data_update_handler, "data_changed")
 
-    def _data_update_handler(self, name, event):
+    def _data_update_handler(self, event):
+        name = event.name
+        data_changed_event = event.new
         # event should be a dict with keys "added", "removed", and "changed",
         # per the comments in AbstractPlotData.
-        if "removed" in event:
-            for name in event["removed"]:
+        if "removed" in data_changed_event:
+            for name in data_changed_event["removed"]:
                 del self.datasources[name]
 
-        if "added" in event:
-            for name in event["added"]:
+        if "added" in data_changed_event:
+            for name in data_changed_event["added"]:
                 self._get_or_create_datasource(name)
 
-        if "changed" in event:
-            for name in event["changed"]:
+        if "changed" in data_changed_event:
+            for name in data_changed_event["changed"]:
                 if name in self.datasources:
                     source = self.datasources[name]
                     source.set_data(self.data.get_data(name))
diff --git a/chaco/plotscrollbar.py b/chaco/plotscrollbar.py
index f17f09978..d434af987 100644
--- a/chaco/plotscrollbar.py
+++ b/chaco/plotscrollbar.py
@@ -148,20 +148,16 @@ def _modify_plot_listeners(self, plot, action="attach"):
             remove=False
         else:
             remove=True
-        plot.on_trait_change(self._component_bounds_handler,
-                             "bounds", remove=remove)
-        plot.on_trait_change(self._component_bounds_handler,
-                             "bounds_items", remove=remove)
-        plot.on_trait_change(self._component_pos_handler,
-                             "position", remove=remove)
-        plot.on_trait_change(self._component_pos_handler,
-                             "position_items", remove=remove)
-
-    def _component_bounds_handler(self):
+        plot.observe(self._component_bounds_handler,
+                     "bounds.items", remove=remove)
+        plot.observe(self._component_pos_handler,
+                     "position.items", remove=remove)
+
+    def _component_bounds_handler(self, event):
         self._handle_dataspace_update()
         self._widget_moved = True
 
-    def _component_pos_handler(self):
+    def _component_pos_handler(self, event):
         self._handle_dataspace_update()
         self._widget_moved = True
 
diff --git a/chaco/scatterplot.py b/chaco/scatterplot.py
index 96f92023f..436ed6414 100644
--- a/chaco/scatterplot.py
+++ b/chaco/scatterplot.py
@@ -521,7 +521,7 @@ def _outline_color_changed(self):
         self.invalidate_draw()
         self.request_redraw()
 
-    def _either_metadata_changed(self):
+    def _either_metadata_updated(self, event):
         if self.show_selection:
             # Only redraw when we are showing the selection. Otherwise, there
             # is nothing to update in response to this event.