This Briefing focuses on the international legal implications of developing and using autonomous weapon systems. Section A considers autonomous weapon systems with respect to the law that governs inter-state use of force (jus ad bellum). Section B considers their legality under the international law of law enforcement. Section C assesses their use in armed conflicts under international humanitarian law, notably in regard to the rules on distinction, proportionality, and precautions in attack. Section D examines the international obligation to conduct a legal review of autonomous weapon systems. Section E considers the issue of accountability. A final section offers brief concluding remarks.