Realism is widely thought of as both the orthodoxy and the classical tradition of thinking about international relations. It is often contrasted to idealism, or more specifically to other so-called paradigms such as liberalism and Marxism. Unfortunately, there is no precise consensus on where the boundaries between these bodies of thought should be drawn. In this chapter I will try to provide an answer to those who have questioned why, given the nature of my writings, I continue to call myself a realist. Doing so will mean that I push the boundaries of realism further out than some people think appropriate. What follows is therefore a rather liberal interpretation. It will emphasise three qualities of realism: its continued relevance, its flexibility in coming to terms with many ideas from other approaches, and its value as a starting point for enquiry. The chapter attempts to provide a compact summary and evaluation of realism as an approach to the study of international relations. It starts by giving a brief overview of the intellectual history, and then sets out the main distinguishing features of realism. Next it looks at the place of realism within the discipline of International Relations, particularly how it relates to other paradigms. It concludes with an evaluation of realism, arguing that it remains the essential core of the subject even though it does not and cannot provide a full understanding of it.