This book primarily discusses the topic of tumor suppressor genes with the help of extensive information. Significant evidence obtained from somatic cell fusion analyses reflect that a group of genes from normal cells might replace or fix a damaged function of cancer cells. Tumorigenesis that could be caused by two mutations was developed by the examination of hereditary retinoblastoma, which led to the eventual cloning of RB1 gene. Ever since, the two-hit hypothesis has helped in isolation of a number of tumor suppressor genes (TSG). Lately, the roles of epigenetic control, haploinsufficiency, and gene dosage impacts in few TSGs, like PTEN, P16 and P53, have been analyzed descriptively. Nowadays, it is commonly recognized that deregulation of growth control is one of the main hallmarks of cancer biological capabilities, and TSGs play vital roles in numerous cellular activities with the help of signaling transduction networks. This book presents a descriptive review of present understanding of TSGs, and demonstrates that the compiled TSG knowledge has given way to a novel frontier for cancer therapies.