Avelumab (Bavencio®) is an intravenously administered programmed cell death ligand-1-blocking human antibody initially developed by EMD Serono Inc. (the biopharmaceutical division of Merck KGaA, Darmstadt, Germany) [now jointly developed and commercialized by EMD Serono Inc. and Pfizer] for the treatment of various tumours. It has received accelerated approval in the USA for the treatment of metastatic Merkel cell carcinoma (mMCC) in adults and paediatric patients aged ≥12 years. The marketing authorization application for avelumab in the treatment of mMCC is undergoing regulatory review in the EU, the biologics license application for avelumab in the treatment of urothelial carcinoma is undergoing priority review by the FDA, and avelumab is in various stages of development internationally for a variety of cancers. This article summarizes the milestones in the development of avelumab leading to this first approval for mMCC.