What do coaches need to know? This paper draws on the literature in expertise development, adult learning and evidence-based practice to offer a fresh perspective on the development of mastery in coaching. In doing so, it goes beyond traditional notions of competencies in suggesting that Mastery = Artistry+ Knowledge+Evidence (MAKE). It offers new ways of thinking about knowledge and evidence in coaching, the Mastery Window as a model for assessing and developing coaches, and some practical steps for coaches wishing to move closer to mastery. This approach places a greater emphasis on the vertical maturation of holistic (inter)personal expertise (the art of coaching) to complement the traditional focus on the horizontal progression of atomised technical expertise (the science of coaching). The conclusion offers insights on five challenges faced by coaching, five trends affecting coaches and implications for the way forward.