Prostate cancer is an androgen dependent disease. Consequently, the mechanism of action of the androgen receptor (AR), the factors that facilitate androgen receptor action, and means to block AR action are of major interest in combating this disease. Studies in the last dozen years have revealed that a remarkable number of proteins and protein complexes interact with AR, thus facilitating its actions as a regulator of transcription. These proteins, termed coactivators, often have intrinsic enzymatic activity or act to recruit other proteins with enzymatic activities that modify chromatin associated proteins, as well as AR, other coactivators and polymerase. Many candidate coactivators have been identified through interaction and overexpression studies. The contributions of some of these to AR activity and prostate cancer cell growth have been further examined in RNA interference studies. This chapter summarizes the current evidence for the roles for these coactivators in prostate cancer based on their contributions to AR action, cell growth and their expression levels in prostate tumors.