Immuno-oncology is an evolving treatment modality that includes immunotherapies designed to harness the patient's own immune system. This approach is being studied for its potential to improve long-term survival across multiple tumor types. It is now important to determine how immunotherapies may be most effectively used to achieve the best possible patient outcomes. Combining or sequencing immunotherapies that target distinct immune pathways is a logical approach, with the potential to further enhance the magnitude of the antitumor immune response over single agents. Early clinical data in patients with melanoma treated with two immune checkpoint inhibitors, ipilimumab and nivolumab, suggest support for this combination approach. Numerous other combination approaches are being evaluated in early-phase clinical trials; however, their clinical activity remains unknown. Clinical experience to date has shown that when combining an immuno-oncology agent with an existing therapeutic modality, it is important to determine the optimal dose, schedule, and sequence. Clin Cancer Res; 20(24); 6258–68. ©2014 AACR.