The retinoblastoma protein (pRb) is one of the key cell-cycle regulating proteins and its inactivation leads to neoplastic transformation and carcinogenesis. This protein regulates critical G1-to-S phase transition through interaction with the E2F family of cell-cycle transcription factors repressing transcription of genes required for this cell-cycle check-point transition. Its activity is regulated through network sensing intracellular and extracellular signals which block or permit phosphorylation (inactivation) of the Rb protein. Mechanisms of Rb-dependent cell-cycle control have been widely studied over the past couple of decades. However, recently it was found that pRb also regulates apoptosis through the same interaction with E2F transcription factors and that Rb-E2F complexes play a role in regulating the transcription of genes involved in differentiation and development.