Pembrolizumab [Keytruda(®) (US)], a humanized monoclonal antibody against the programmed death receptor-1 (PD-1) protein, has been developed by Merck & Co for the treatment of cancer. Pembrolizumab has received its first global approval for the treatment of advanced, unresectable or metastatic malignant melanoma in the US, for use in patients with disease progression after prior treatment with ipilimumab and, for BRAF V600 mutation-positive patients, a BRAF inhibitor. It is the first anti-PD-1 therapy to receive regulatory approval in the US, and is currently under regulatory review in the EU. This article summarizes the milestones in the development of pembrolizumab leading to this first approval for the treatment of malignant melanoma.