Of all the strategies and systems surveyed in this book, only the United Nations currently exists. Imperfect and incomplete though it is, the UN provides us with a living laboratory in which to trace the evolution of a concept of security from theory into practice amid the often dismaying realities of global power politics. If the UN has thus far failed to accomplish much of the task assigned it by its founders, a careful study of the sources of its failures—as well as a recognition of its neglected successes—may help us to judge what will and will not work in the various alternatives explored in this book. In the process, it may also help us rescue and revive what is still worth preserving in the UN system itself.