Immune checkpoint inhibitors have become standard of care for multiple tumour types. Two classes of agents have been approved for clinical use: CTLA-4 and PD-1/PD-L1. This article discusses the rationale behind why CTLA-4 and PD-1/PD-L1 inhibitors are beneficial for cancer therapy, their potential shortcomings, and why new agents and strategies are needed to broaden their therapeutic scope.