This is a completely revised and updated edition of a book originally published in 2004 and revised in 2010. In the interval, the law of international armed conflict has not stood still. State practice has grown, new case law has emerged, and there has been a constant outflow of additional books, essays and notes about the conduct of hostilities. There is growing interest in developing weapon technologies (such as cyber and drones), but perennial issues – like urban warfare – also tend to raise novel complex issues.

The book has greatly benefited from being used as a teaching tool in a number of classrooms, both in law schools and in military colleges, in several countries. This has led to substantial feedback by way of comments and queries pressing for further elucidation of contentious points. It is hoped that the present edition will provide adequate answers and shed further light on the lex lata.

By now, the present volume serves as a companion to three other books printed by Cambridge University Press, dealing respectively with the jus ad bellum, the law of belligerent occupation, and non-international armed conflicts. Broadly speaking, between them, the four publications cover the general spectrum of the law of armed conflict in its various aspects. Every effort has been made to minimize repetition, and matters explored in detail in the complementary works are not rehashed here.

To facilitate syntax, generic pronouns relating to individual combatants or civilians are usually drawn in masculine form. This must not be viewed as gender-specific.