Autonomous weapons systems select and apply force to targets based on sensor processing rather than human input. Some autonomous weapons systems have existed for years, but the types, duration of operation, geographical scope, and environment in which such systems operate have been limited. Now technological advances are spurring the development of autonomous weapons systems or "killer robots," which would operate without meaningful human control, delegating life-and-death decisions to machines. Such weapons systems raise serious ethical, moral, legal, accountability, and security problems and concerns. Human Rights Watch is a founding member of Stop Killer Robots campaign, a civil society coalition that calls for a new international treaty to prohibit and restrict autonomous weapons systems.