Eight members comprise the Inhibitor of apoptosis (IAP) family in humans: NAIP/BIRC1, cIAP1/BIRC2, cIAP2/BIRC3, XIAP/BIRC4, Survivin/BIRC5, BIRC6, Livin/BIRC7, and BIRC8. These related proteins commonly share a baculorvirus IAP repeat (BIR) domain, an 80-residue zinc-binding domain that mediates protein-protein interactions. Some members also share a C-terminal RING domain that confers an E3 ubiquitin ligase activity. The IAP proteins are most known for negative regulation of apoptosis by inhibitory binding to caspases or ubiquitination of pro-apoptotic kinase RIP1. Aside from apoptosis, IAPs promote cell proliferation through activation of NF-κB and MAPK signaling pathways. Furthermore, they are overexpressed in several tumour types, making them very attractive targets for cancer therapy.