The tumor susceptibility gene 101 (TSG101) encodes a multidomain protein that contains a UEV (ubiquitin e2 variant) domain at is N-terminus and a putative DNA-binding motif at its C-terminus. In addition to being a bona fide component of the ESCRT (endosomal sorting complexes required for transport) complex 1 and playing a critical role in endosomal sorting and trafficking, TSG101 has also been implicated in an array of cellular functions including, cytokinesis, protein ubiquitination, transcriptional regulation, cell cycle and proliferation, as well as viral budding. The major focus of this article is on the role of TSG101 in tumorigenesis.