diff --git a/toolz/itertoolz.py b/toolz/itertoolz.py
index 941b9a9f..6fb03967 100644
--- a/toolz/itertoolz.py
+++ b/toolz/itertoolz.py
@@ -809,13 +809,74 @@ def getter(index):
         return operator.itemgetter(index)
 
 
+def _inner_join(leftkey, leftseq, rightkey, rightseq):
+    d = groupby(leftkey, leftseq)
+    for item in rightseq:
+        key = rightkey(item)
+        if key in d:
+            for left_match in d[key]:
+                yield (left_match, item)
+
+
+def _right_join(leftkey, leftseq, rightkey, rightseq,
+                left_default=no_default):
+    d = groupby(leftkey, leftseq)
+    for item in rightseq:
+        key = rightkey(item)
+        if key in d:
+            for left_match in d[key]:
+                yield (left_match, item)
+        else:
+            yield (left_default, item)
+
+
+def _left_join(leftkey, leftseq, rightkey, rightseq,
+               right_default=no_default):
+    d = groupby(leftkey, leftseq)
+    seen_keys = set()
+    for item in rightseq:
+        key = rightkey(item)
+        seen_keys.add(key)
+        if key in d:
+            for left_match in d[key]:
+                yield(left_match, item)
+
+    for key, matches in iteritems(d):
+        if key not in seen_keys:
+            for match in matches:
+                yield (match, right_default)
+
+
+def _full_join(leftkey, leftseq, rightkey, rightseq,
+               left_default=no_default, right_default=no_default):
+    d = groupby(leftkey, leftseq)
+    seen_keys = set()
+    for item in rightseq:
+        key = rightkey(item)
+        seen_keys.add(key)
+        if key in d:
+            for left_match in d[key]:
+                yield (left_match, item)
+        else:
+            yield (left_default, item)
+
+    for key, matches in iteritems(d):
+        if key not in seen_keys:
+            for match in matches:
+                yield (match, right_default)
+
+
 def join(leftkey, leftseq, rightkey, rightseq,
          left_default=no_default, right_default=no_default):
     """ Join two sequences on common attributes
 
     This is a semi-streaming operation.  The LEFT sequence is fully evaluated
-    and placed into memory.  The RIGHT sequence is evaluated lazily and so can
-    be arbitrarily large.
+    and placed into memory.  The RIGHT sequence is evaluated lazily and unless
+    right_default is defined, it can be arbitrarily large.  If right_default is
+    defined, the unique keys of rightseq will be placed into memory.
+    The join is implemented as a hash join and the keys of leftseq must be
+    hashable. Additionally, if right_default is defined, then keys of rightseq
+    must also be hashable.
 
     >>> friends = [('Alice', 'Edith'),
     ...            ('Alice', 'Zhao'),
@@ -868,26 +929,18 @@ def join(leftkey, leftseq, rightkey, rightseq,
     if not callable(rightkey):
         rightkey = getter(rightkey)
 
-    d = groupby(leftkey, leftseq)
-    seen_keys = set()
-
-    left_default_is_no_default = (left_default == no_default)
-    for item in rightseq:
-        key = rightkey(item)
-        seen_keys.add(key)
-        try:
-            left_matches = d[key]
-            for match in left_matches:
-                yield (match, item)
-        except KeyError:
-            if not left_default_is_no_default:
-                yield (left_default, item)
-
-    if right_default != no_default:
-        for key, matches in d.items():
-            if key not in seen_keys:
-                for match in matches:
-                    yield (match, right_default)
+    if (left_default == no_default) and (right_default == no_default):
+        return _inner_join(leftkey, leftseq, rightkey, rightseq)
+    elif (left_default != no_default) and (right_default == no_default):
+        return _right_join(leftkey, leftseq, rightkey, rightseq,
+                           left_default=left_default)
+    elif (left_default == no_default) and (right_default != no_default):
+        return _left_join(leftkey, leftseq, rightkey, rightseq,
+                          right_default=right_default)
+    else:
+        return _full_join(leftkey, leftseq, rightkey, rightseq,
+                          left_default=left_default,
+                          right_default=right_default)
 
 
 def diff(*seqs, **kwargs):