This title was first published in 2003. We may have witnessed the partial erosion of the classical view that the international legal system is horizontal and consensual, but to argue that legal regulation can occur in relation to the ultimate expression of high politics - the use of military power - attracts accusations of 'idealism'. Maybe it is too much to expect law and institutions to govern or regulate the use of force in international relations, though it can be argued that legal issues are significant in shaping the debate. Whether a powerful State can take military action against another without the authority of the Security Council, is, for instance, both a political and a legal issue. Though the law may not be controlling, it can provide a counterbalance to political choice. The essays in this volume illustrate the profound differences that exist as to the existence, role, and efficacy of collective security law.