Updated throughout for its second edition, this book explores collective security as practised within the legal framework provided by the United Nations Charter, with a particular focus upon activity undertaken under the auspices of the UN Security Council for the maintenance of international peace and security.

This new edition follows a decade of new developments in the areas covered by the first edition, both in respect of the UN's practices under its collective security system and the wider international context within which it operates. Taking account of the Russia-Ukraine conflict and Syrian Civil War, the book additionally covers debates over UNSC reform and conceptualisations of the collective security concept. Offering a comprehensive analysis, it considers the full range of measures which can be utilised by the UN in the performance of its collective security remit, including military enforcement action, peacekeeping, non-military sanctions and diplomacy. The book considers each of these measures in detail, assessing the legal framework applicable to the form of action, the main legal controversies which arise in respect of their appropriate utilisation and the UN's use of this collective security 'tool' in practice. The book draws conclusions about the main strengths and shortcomings of the various means through which the UN can attempt to prevent, minimise or end conflict.

The book will be of interest to researchers in the fields of international law, international relations and modern international history.