Caveolae ('little caves') are plasma membrane specializations of 50-100 nm in diameter, and the caveolins are structural proteins used by cells to form caveolae. We and other investigators have discovered that caveolae organelles may be important both in normal signal transduction and in the pathogenesis of a number of human diseases, such as cancer. Here we describe the functional roles of the caveolin gene family and summarize the evidence that supports a role for caveolae as mediators of a number of cellular signalling processes, including apoptosis.