Political realism is a highly diverse body of international relations theory. This substantial reference work examines political realism in terms of its history, its scientific methodology and its normative role in international affairs. Split into three sections, it covers the 2000-year canon of the different schools of thought, the key thinkers and how it responds to foreign policy challenges faced by individual states and globally. It brings political realism up-to-date by showing where theory has failed to keep up with contemporary problems and suggests how it can be applied and adapted to fit our new, globalised world order.