RBBP8, also known as CtBP (carboxy-terminal binding protein) interacting protein (CTIP), was characterized for its role in transcription as a cofactor for the transcriptional repressor CtBP, and also as a binding partner for other proteins including the cell cycle regulators retinoblastoma protein (Rb) and breast cancer 1 (BRCA1). It is ubiquitously expressed and localizes to the nucleus. RBBP8 is thought to modulate the functions in cell proliferation, transcriptional regulation and DNA repair. RBBP8 also plays a central role in the cell cycle checkpoint response to DNA double-stranded breaks (DSBs), with new evidence demonstrating that it controls the choice of DSB repair pathway.