The United Nations Security Council is meant to be the central international organ for maintaining international peace and security, and it has a profound impact on the rights and duties of states under international law. However, it has been severely criticized throughout its existence. This book examines the role of international law in its decisions and decision-making process since the end of the Cold War, with the principle of legality as theoretical framework. It explores the limits that international law places on the Security Council, i.e. what it is allowed to demand of and impose on states. More importantly, however, this study provides great insight into how states use international legal arguments in the Council’s decision-making process, and whether the Security Council has in practice respected and observed these legal limits. Selected case studies include Iraq, the former Yugoslavia, Haiti, East Timor and international terrorism.