In 2004, the Report of the Secretary-General’s High-Level Panel on Threats, Challenges and Change emphasised the linkages between economic development, security and human rights, and the imperative in the twenty-first century of collective action and cooperation between States. In a world deeply divided by differences of power, wealth, culture and ideology, central questions today in international law and organisation are whether reaffirmation of the concept of collective security and a workable consensus on the means of its realisation are possible. In addressing these questions, this book considers the three key documents in the recent UN reform process: the High-Level Panel report, the Secretary-General’s In Larger Freedom report and the 2005 World Summit Outcome document. The chapters examine the responsibilities, commitments, strategies and institutions necessary for collective security to function both in practice and as a normative ideal in international law and relations between state and non-state actors alike.