For policymakers, this book explains the ramifications under international humanitarian law of a major new field of weapon development with a focus on questions currently being debated by governments, the United Nations and other bodies. Based on a clear explanation of the principles of autonomous systems and a survey of technologies under active development as well as some that are in use today, it provides a thorough legal analysis grounded on a clear understanding of the technological realities of autonomous weapon systems. For legal practitioners and scholars, it describes the legal constraints that will apply to use of autonomous systems in armed conflict and the measures that will be needed to ensure that the efficacy of the law is maintained. More generally, it serves as a case study in identifying the legal consequences of use of autonomous systems in partnership with, or in place of, human beings.