Ra-223 (radium-223) is an alpha particle-emitting radiopharmaceutical with targeted uptake in areas of osteoblastic lesions. The combination of targeted skeletal uptake, short tissue-penetration range, and high energy of alpha particles allows for targeted cell killing and a low toxicity profile. A phase III trial (ALSYMPCA) demonstrated improvements in overall survival and symptomatic skeletal events in patients with castration-resistant prostate cancer and multifocal symptomatic bone metastases. Adverse events were limited but included both gastrointestinal and hematologic effects. This article will describe the historic background of Ra-223; outline the clinical studies which led to phase III trials of this agent; highlight key results of these phase III studies; and explore possible future directions for use of Ra-223 and other alpha particles--both in prostate cancer and for management of other diseases.