Proton therapy has been used in the treatment of cancer for over 50 years. Due to its unique dose distribution with its spread-out Bragg peak, proton therapy can deliver highly conformal radiation to cancers located adjacent to critical normal structures. One of the important applications of its use is in prostate cancer, since the prostate is located adjacent to the rectum and bladder. Over 30 years of data have been published on the use of proton therapy in prostate cancer; these data have demonstrated high rates of local and biochemical control as well as low rates of urinary and rectal toxicity. Although before 2000 proton therapy was available at only a couple of centers in the United States, several new proton centers have been built in the last decade. With the increased availability of proton therapy, research on its use for prostate cancer has accelerated rapidly. Current research includes explorations of dose escalation, hypofractionation, and patient-reported quality-of-life outcomes. Early results from these studies are promising and will likely help make proton therapy for the treatment of prostate cancer more cost-effective.