The emergence of immuno-oncology therapies, which modify the activity of a patient’s immune system with the aim of eliminating cancer cells, has prompted a paradigm shift in the treatment of many cancer types. Following the launch of the first immune checkpoint inhibitor Yervoy® (ipilimumab) by Bristol-Myers Squibb (BMS) in 2011, the growth of the immuno-oncology market has predominantly been driven by checkpoint inhibitors with PD-1 (programmed cell death-1) and PD-L1 (protein death ligand-1) mechanisms of action that have broad efficacy across a number of solid tumours. Late 2014 saw the market introductions of BMS/Ono Pharmaceutical’s Opdivo® (nivolumab) and Merck & Co.’s Keytruda® (pembrolizumab), two highly anticipated PD-1 targeted agents that have seen rapid uptake owing to their impressive clinical profile. This paper reviews the trends in M&A and partnering in immuno-oncology since 2013.