Dr Tom Ruys is a lawyer with Stibbe, Brussels, and a senior member of the Leuven Centre for Global Governance Studies. He also teaches public international law and humanitarian and security law as a substitute lecturer at the Catholic University of Leuven.

• Introduction; 1. The methodological debate and the quest for custom; 2. Conditions of self-defence; 3. The Armed Attack Requirement Ratione Materiae; 4. The Armed Attack Requirement Ratione Temporis; 5. The Armed Attack Requirement Ratione Personae; 6. What future for the armed attack criterion?

'… a great strength of the book is that it provides a detailed restatement of the law on self-defence and the crucial issues surrounding it … Ruys' work demonstrates a large amount of research into the content of the customary law, using both an 'incident analysis' approach and a consideration of practice in abstracto (for example, in relation to debates over various UN declarations). This research into state practice is of notable breadth and depth, and forms the cornerstone on which all the book's analysis is built … this is an excellent book on armed attack …' James A. Green, Journal of Conflict and Security Law