Apoptosis is a physiologic mechanism of cell death that is induced during development or reversible tissue expansion or after tissue damage to eliminate unwanted cells. Recently, viral gene products have been shown to either specifically induce or specifically inhibit apoptosis. In this review, our current understanding of the regulation of apoptosis is outlined. The mechanisms by which viruses can inhibit or induce apoptosis are described. The role of apoptosis in modulating the immune response to viral infection is discussed. Finally, the hypothesis is advanced that the balance between induction and inhibition of apoptosis is modulated by viruses to optimize the course of viral infection.