Survivin (BIRC5 or IAP4) is the smallest member of inhibitors of apoptosis proteins (X-linked IAP/XIAP, c-IAP1, c-IAP2, IAP-like protein-2/ ILP2, melanoma IAP/ ML-IAP, Livin, NAIP, and survivin) and besides its anti-apoptotic functions; survivin also regulates processes such as cell cycle, migration, metastasis etc. Highly critical in fetal development, survivin is generally no longer present in adult tissues; however, its re-expression occurs in cancers wherein it drives proliferation, metastasis, poor prognosis, and decreased patient survival. Survivin contains only one copy of a modified baculovirus IAP repeat (BIR, a domain required for caspases inactivation) which is used for homodimerization and for its interaction with other chromosome passenger proteins. Phosphorylation/mutation of Thr-48 in the BIR domain affects survivin's dual ability to inhibit apoptosis and regulate cell division. Under apoptotic stimuli involving mitochondria, survivin forms a complex with XIAP, thus increasing the stability of XIAP and its inhibitory activity against caspases. The survivin binding to mitochondrial Smac/DIABLO leads to a delayed Smac/DIABLO release in the cytoplasm resulting in prolonged cell survival. Survivin-HBXIP complex can bind to pro-caspase-9 for exerting prevention of mitochondrial apoptosis activation. For facilitating correct cell division, survivin recognize/complex with phospho-histone-H3 and associates with the chromosome passenger proteins (Aurora B, INCENP, and borealin) and this new complex is recruited to the mitotic centromers where it assists/ensure proper chromosomal segregation. Moreover, at the centrosomes of dividing cells, survivin binds to Cdk1 which is critical for cells to enter mitosis.