Associations between the cytoskeleton and cellular membranes, both within the cell and at points of cell contact, play a central role in determining cell shape and tissue integrity. During the past few years, it has become clear that many of these cytoskeleton-membrane interactions go far beyond simple mechanical linkages. For example, proteins that act as linker molecules at the adherens junctions and desmosomes in the plasma membrane have newly recognized functions in signal transduction pathways. These functions have profound effects on cell behaviour during development. In addition, within the nucleus, the lamin branch of the intermediate filament protein family appears to have a key role in defining the protein composition of the inner nuclear membrane by means of extensive interactions with integral membrane proteins. The identities of these integral membrane proteins are only now coming to light.