Mast cell tumours (MCTs) are common tumours in dogs. They mainly affect the skin, although they can affect other tissues and organs. In recent years, there have been significant advances in predicting skin MCT behaviour and treatment, including the licensing of two tyrosine kinase inhibitors for the treatment of this condition. This article focuses on skin (cutaneous and subcutaneous) MCTs. It summarises current understanding of MCT behaviour, prognosis and treatment, with a particular focus on treatment decision-making. James Warland graduated from the University of Cambridge in 2009. He recently completed a ECVIM residency in small animal internal medicine at Cambridge. Valentina Brioschi qualified from the University of Milan in 2005.She is currently completing a three-year residency in small animal surgery at Cambridge university.