diff --git a/taskflow/engines/action_engine/runtime.py b/taskflow/engines/action_engine/runtime.py
index 395ce750..a04808da 100644
--- a/taskflow/engines/action_engine/runtime.py
+++ b/taskflow/engines/action_engine/runtime.py
@@ -38,7 +38,7 @@ class Runtime(object):
         self._task_executor = task_executor
         self._storage = storage
         self._compilation = compilation
-        self._scopes = {}
+        self._walkers_to_names = {}
 
     @property
     def compilation(self):
@@ -76,9 +76,9 @@ class Runtime(object):
                              self._task_executor)
 
     def fetch_scopes_for(self, atom_name):
-        """Fetches a tuple of the visible scopes for the given atom."""
+        """Fetches a walker of the visible scopes for the given atom."""
         try:
-            return self._scopes[atom_name]
+            return self._walkers_to_names[atom_name]
         except KeyError:
             atom = None
             for node in self.analyzer.iterate_all_nodes():
@@ -88,10 +88,10 @@ class Runtime(object):
             if atom is not None:
                 walker = sc.ScopeWalker(self.compilation, atom,
                                         names_only=True)
-                self._scopes[atom_name] = visible_to = tuple(walker)
+                self._walkers_to_names[atom_name] = walker
             else:
-                visible_to = tuple([])
-            return visible_to
+                walker = None
+            return walker
 
     # Various helper methods used by the runtime components; not for public
     # consumption...
diff --git a/taskflow/engines/action_engine/scopes.py b/taskflow/engines/action_engine/scopes.py
index c55305d0..99e1578b 100644
--- a/taskflow/engines/action_engine/scopes.py
+++ b/taskflow/engines/action_engine/scopes.py
@@ -56,9 +56,14 @@ class ScopeWalker(object):
         if self._node is None:
             raise ValueError("Unable to find atom '%s' in compilation"
                              " hierarchy" % atom)
+        self._level_cache = {}
         self._atom = atom
         self._graph = compilation.execution_graph
         self._names_only = names_only
+        self._predecessors = None
+
+    #: Function that extracts the *associated* atoms of a given tree node.
+    _extract_atoms = staticmethod(_extract_atoms)
 
     def __iter__(self):
         """Iterates over the visible scopes.
@@ -95,27 +100,34 @@ class ScopeWalker(object):
         nodes (aka we have reached the top of the tree) or we run out of
         predecessors.
         """
-        predecessors = set(self._graph.bfs_predecessors_iter(self._atom))
+        if self._predecessors is None:
+            pred_iter = self._graph.bfs_predecessors_iter(self._atom)
+            self._predecessors = set(pred_iter)
+        predecessors = self._predecessors.copy()
         last = self._node
-        for parent in self._node.path_iter(include_self=False):
+        for lvl, parent in enumerate(self._node.path_iter(include_self=False)):
             if not predecessors:
                 break
             last_idx = parent.index(last.item)
-            visible = []
-            for a in _extract_atoms(parent, idx=last_idx):
-                if a in predecessors:
-                    predecessors.remove(a)
-                    if not self._names_only:
+            try:
+                visible, removals = self._level_cache[lvl]
+                predecessors = predecessors - removals
+            except KeyError:
+                visible = []
+                removals = set()
+                for a in self._extract_atoms(parent, idx=last_idx):
+                    if a in predecessors:
+                        predecessors.remove(a)
+                        removals.add(a)
                         visible.append(a)
-                    else:
-                        visible.append(a.name)
-            if LOG.isEnabledFor(logging.BLATHER):
-                if not self._names_only:
+                self._level_cache[lvl] = (visible, removals)
+                if LOG.isEnabledFor(logging.BLATHER):
                     visible_names = [a.name for a in visible]
-                else:
-                    visible_names = visible
-                LOG.blather("Scope visible to '%s' (limited by parent '%s'"
-                            " index < %s) is: %s", self._atom,
-                            parent.item.name, last_idx, visible_names)
-            yield visible
+                    LOG.blather("Scope visible to '%s' (limited by parent '%s'"
+                                " index < %s) is: %s", self._atom,
+                                parent.item.name, last_idx, visible_names)
+            if self._names_only:
+                yield [a.name for a in visible]
+            else:
+                yield visible
             last = parent