The inhibitor of apoptosis protein (IAP) family consists of an evolutionarily conserved group of apoptosis inhibitors containing a conserved 70 amino acid BIR (baculovirus inhibitor repeat) domain. Human members of this family include c-IAP1, c-IAP2, XIAP, survivin, livin, and NAIP. Overexpression of IAP family members, particularly survivin and livin, in cancer cell lines and primary tumors suggests an important role for these proteins in cancer progression. In general, the IAP proteins function through direct interactions to inhibit the activity of several caspases, including caspase-3, caspase-7, and caspase-9. In addition, binding of IAP family members to the mitochondrial protein Smac blocks their interaction with caspase-9, thereby allowing the processing and activation of the caspase.