Prostate cancer is among the most common malignancies in Western countries, and its incidence is rapidly rising in Asia where it was traditionally considered an uncommon tumor. Our understanding of the disease and management strategies continue to evolve. The first revolution of its treatment was in the 1940s when hormonal therapy was used to treat patients. The discovery of prostate-specific antigen (PSA) and the subsequent adoption of widespread PSA screening have made it possible to diagnose the disease early, but it was not until recently that the field realized that we had been overdiagnosing and overtreating a large number of men with indolent diseases that will not impact their quality of life or life expectancy. Distinguishing indolent tumors from aggressive ones remains a challenge, although recent advances in multiparametric MRI have given clinicians more confidence in choosing men for active surveillance. However, more need to be done to fundamentally understand the molecular and cellular bases that determine the biologic behavior of each of the tumors.