Our immune system is characterized by remarkable specificity, potency, and memory -- the ability of a single vaccine treatment to provide life-long protection. No pharmacologic treatment for any indication can provide the same level of safety, efficacy, and long-lasting effect that a vaccine can. Thus, researchers and clinicians alike have sought to apply these characteristics to the treatment of cancer. Yet, for the last 125 years, the field has failed to realize this potential. Here, we will review some of the most promising cancer immunotherapeutic approaches in development today, as recent clinical successes signal the beginning of cancer immuno-therapy's transition from experimental to established therapy.