Androgen refractory prostate cancer metastasis is a major clinical challenge. Mechanism-based approaches to treating prostate cancer metastasis require an understanding of the developmental origin of the metastasis-initiating cell. Properties of prostate cancer metastases such as plasticity with respect to differentiated phenotype and androgen independence are consistent with the transformation of a prostate epithelial progenitor or stem cell leading to metastasis. This review focuses upon current evidence and concepts addressing the identification and properties of normal prostate stem or progenitor cells and their transformed counterparts.