Androgen receptor (AR) is a member of the ligand activated transcription factor family. Its function is regulated by a complex network of coregulatory proteins and cell signaling pathways. AR is a key transcription factor in healthy prostate function and during neoplastic transformation. In normal prostate, it regulates prostate secretory function, stimulates epithelial cell renewal, and maintains the cells in a differentiated state. However, under certain circumstances AR function loses its differentiating thrust and proliferative function becomes dominant. Changes in coregulator expression and alteration of cell signaling pathways may contribute to changes in androgen-dependent AR action and play a major role in castration resistant prostate cancer (CRPC).