Many governmental policies are justified by the need to protect national security. But the concept of security is often underspecified in this context. If nothing else, security involves freedom from (significant) risks of harm. But should we expand our conception of security to include other elements? This paper argues that, in answering this question, we need to consider the role that security plays in politics. It defends a conception of security that locates its value primarily in the protection of the (...) autonomy of individuals. While this explains why various risks of harm should be viewed as set-backs to security, other sorts of threats will also be included. Finally, it considers the implications of this account for questions of security policy. It is claimed that international cooperation on security matters, far from the optional policies they are often viewed as, may in fact be necessary for states to be legitimate. (shrink)