The figure of the "professional" looms large in our contemporary society as an ideal for economic activity and socio-political inclusion, and even as a model for individual self-development. But how and when did this figure arise? And what has led professional activity to become such an essential part of our personal, social, moral, economic, and political life? While Max Weber and others have famously addressed these questions, this book reveals a more nuanced history of the concept of "profession" and "professional duty," and offers the first comprehensive study of the discourse of professional ethics from a historical perspective. Italy, France, Germany, and the United Kingdom provide most of the rich corpus of philosophical, juridical, and theological sources discussed throughout the book in its longue durée journey from Ancient Rome to the present.