The educational opportunities and qualifications, corporate structures and regulation that had become accepted features of the Irish medical profession in the era of Charles Lucas were the fruits of a slow process of professionalization initiated by a handful of Irish medics who, from the 1620s, began tackling poor standards of medical practice in an era of medical pluralism. This paper begins by reviewing the standard of practice in early seventeenth- century Ireland. Through the examples of Thomas Arthur, M.D. and John Clavell, a self-styled medic, differences in the approaches adopted by university-trained physicians and unorthodox practitioners are highlighted. The succession of significant steps taken in this professionalization process are traced, with particular emphasis on the failed attempt to establish a Royal College of Physicians in Dublin during the mid-1620s and the importance of the influx of English physicians in the 1650s for the creation of permanent corporate structures and regulation.