Michael Sheehan provides a masterly survey of the varied positions that scholars have adopted in interpreting security, one of the most contested terms in international relations, and asks whether a synthesis is possible that both widens and deepens our understanding of the concept. Sheehan begins by outlining the classical realist approach of Morgenthau and Carr and the ideas of their neorealist heirs. He then explores how the economic security approach embraces both defense economics and human security from poverty and hunger; and how environmental security links environment and security in a fundamental challenge to the international political hierarchy. Next, tackling the various postpositivist perspectives on security, all of which stem from worldviews fundamentally different from that of realism, he explains the range of feminist thought on security, the ideas of the critical security school, and the main concerns of postmodern security theory. In conclusion, revealing his own interpretation of security, he makes the case for a postpositivist conception that links human emancipation, justice, and peace.