The immunological synapse (IS) has proved to be a stimulating concept, particularly in provoking discussion on the similarity of intercellular communication controlling disparate biological processes. Recent studies have clarified some of the underlying molecular mechanisms and functions of the IS. For both T cells and natural killer (NK) cells, assembly of the IS can be described in stages with distinct cytoskeletal requirements. Functions of the IS vary with circumstance and include directing secretion and integrating positive and negative signals to determine the extent of response.