Lethal autonomous weapons (LAWs) are a type of military drone or military robot which are autonomous in that they can independently search for and engage targets based on programmed constraints and descriptions. As of 2025, most military drones and military robots are not truly autonomous. LAWs are also known as lethal autonomous weapon systems (LAWS), autonomous weapon systems (AWS), robotic weapons or killer robots. LAWs may engage in drone warfare in the air, on land, on water, underwater, or in space.

In weapons development, the term "autonomous" is somewhat ambiguous and can vary hugely between different scholars, nations and organizations.

The official United States Department of Defense Policy on Autonomy in Weapon Systems defines an Autonomous Weapons System as one that "...once activated, can select and engage targets without further intervention by a human operator." Heather Roff, a writer for Case Western Reserve University School of Law, describes autonomous weapon systems as "... capable of learning and adapting their 'functioning in response to changing circumstances in the environment in which [they are] deployed,' as well as capable of making firing decisions on their own."

The British Ministry of Defence defines autonomous weapon systems as "systems that are capable of understanding higher level intent and direction. From this understanding and its perception of its environment, such a system is able to take appropriate action to bring about a desired state. It is capable of deciding a course of action, from a number of alternatives, without depending on human oversight and control - such human engagement with the system may still be present, though. While the overall activity of an autonomous unmanned aircraft will be predictable, individual actions may not be."

Scholars such as Peter Asaro and Mark Gubrud believe that any weapon system that is capable of releasing a lethal force without the operation, decision, or confirmation of a human supervisor can be deemed autonomous.

Creating treaties between states requires a commonly accepted labeling of what exactly constitutes an autonomous weapon.

The oldest automatically triggered lethal weapon is the land mine, used since at least the 1600s, and naval mines, used since at least the 1700s.

Some current examples of LAWs are automated "hardkill" active protection systems, such as a radar-guided CIWS systems used to defend ships that have been in use since the 1970s (e.g., the US Phalanx CIWS). Such systems can autonomously identify and attack oncoming missiles, rockets, artillery fire, aircraft, and surface vessels according to criteria set by the human operator. Similar systems exist for tanks, such as the Russian Arena, the Israeli Trophy, and the German AMAP-ADS. Several types of stationary sentry guns, which can fire at humans and vehicles, are used in South Korea and Israel. Many missile defence systems, such as Iron Dome, also have autonomous targeting capabilities.