The iap family of anti-apoptotic genes, originally discovered in viruses, has grown considerably ipl the past two years with the addition of a number of evolutionarily conserved cellular homologues. Although the mechanism(s) by which these novel proteins block cell death is still unknown, intriguing clues to their function have been revealed by the discovery of interactions between Some of the IAP homologues and cellular proteins involved in carrying out apoptotic signalling. Here, Rollie Clem and Colin Duckett discuss how the various IAP proteins may function in regulating apoptosis.