This dissertation aims to demonstrate that a new type of peace operation, here called "peace enforcement", has been recognized in theory and practice, and to describe its features in detail. As an analysis of UN documentation (chapter 1), selected cases (chapters 2-5) and national military doctrine shows, peace enforcement combines features of both traditional peace-keeping and the kind of large-scale enforcement action that has been mounted in cases of transboundary aggression (e.g. the Persian Gulf, 1990-91). The last three sections of the dissertation are devoted to elaborating a definition of peace enforcement - first from a political perspective (its operational characteristics, chapter 7), then from a legal one (its legal basis, chapter 8) - and to sketching out its role in relation to other types of peace operation