Metastatic castration-resistant prostate cancer is the lethal form of cancer of the prostate. Five new agents that prolong survival in this group have emerged in the past 5 years, and sipuleucel-T is among them. Sipuleucel-T is the only immunotherapy shown to improve survival in prostate cancer. It is currently indicated in asymptomatic or mildly symptomatic patients, as it has never shown a direct cancer effect. This paper describes the process of creating the sipuleucel-T product from the manufacturing and patient aspects. It discusses the four placebo-controlled, randomized clinical trials (RCTs) of sipuleucel-T, focusing on survival and adverse events. There are three RCTs in metastatic castration-resistant prostate cancer, all of which showed improved overall survival without meaningful decreases in symptoms, tumor volumes, or prostate-specific antigen levels. One RCT in castration-sensitive, biochemically relapsed prostate cancer attempted to find a decrease in biochemical failure, but that endpoint was not reached. Adverse events in all four of these studies centered around cytokine release. This paper also reviews a Phase II study of sipuleucel-T given neoadjuvantly that speaks to its mechanism of action. Additionally, there is a registry study of sipuleucel-T that has been used to evaluate immunological parameters of the product in men ≥80 years of age and men who had previously been treated with palliative radiation. Attempts to find early markers of response to sipuleucel-T are described. Further ongoing studies that explore the efficacy of sipuleucel-T in combination with immune checkpoint inhibitors and second-generation hormonal therapies that are summarized. Finally, the only published economic analysis of sipuleucel-T is discussed.