What impact did the Hippocratic tradition have on the development of medical knowledge and practice? For some, that tradition, beginning with its founder Hippocrates, provides a framework for understanding the development of contemporary western medicine – particularly a rational, scientific endeavor – that is evidence-based. Moreover, the Hippocratic tradition is not only important in terms of the development of medical knowledge but also its practice, as exemplified by the Hippocratic oath. For others, however, the development of contemporary western medicine represents a rejection not so much of the founder of the Hippocratic tradition but of the tradition itself, especially its vitalism and humoral theory of health and disease. In this chapter, the impact of the Hippocratic tradition on the development of medical knowledge is examined first, followed by an exploration of how the tradition, particularly the Hippocratic oath, shaped medical practice. The chapter concludes with a discussion of the lessons this investigation into the Hippocratic tradition’s impact on the development of western medicine teach us about the future of western medicine with respect to its knowledge and practice in the twenty-first century.