Galen conceived of philosophy not as an intellectual exercise, but as a way of life; and this attitude was also in tune with the eclecticism of his times. In medicine and philosophy, Galen disavowed school allegiances, likening them to slavery; and while he adopts and adapts elements from the leading schools of the time, Stoic, Epicurean, Peripatetic and Platonist, he is no mere intellectual magpie, flitting randomly from one source to another. While philosophy and medicine are intimately linked, it would be a mistake to suppose that for him philosophy invariably plays a purely instrumental, subsidiary role. This chapter focuses on this complex and multi-faceted picture organized around Galen's attitude and contributions to the three canonical parts of the discipline. The three canonical branches of philosophy are logic, physics, and ethics. Galen also wrote numerous particular tracts on logical issues, as well as several volumes of commentary on Aristotle, the Stoics and others, none of which survive either.