Non-lethal weapons, also called nonlethal weapons, less-lethal weapons, less-than-lethal weapons, non-deadly weapons, compliance weapons, or pain-inducing weapons are weapons intended to be less likely to kill a living target than conventional weapons such as knives and firearms with live ammunition. It is often understood that unintended or incidental casualties are risked wherever force is applied, but non-lethal weapons try to minimise the risk of casualties (e.g. serious/permanent injuries or death) as much as possible. Non-lethal weapons are used in policing and combat situations to limit the escalation of conflict where employment of lethal force is prohibited or undesirable, where rules of engagement require minimum casualties, or where policy restricts the use of conventional force. These weapons occasionally cause serious injuries or death; the term "less-lethal" has been preferred by some organizations as it describes the risks of death more accurately than the term "non-lethal", which some have argued is a misnomer.
Non-lethal weapons may be used by conventional military in a range of missions across the force continuum. They may also be used by military police, by United Nations forces, and by occupation forces for peacekeeping and stability operations. Non-lethal weapons may also be used to channelize a battlefield, control the movement of civilian populations, or to limit civilian access to restricted areas (as they were utilized by the USMC's 1st Marine Expeditionary Force in Somalia in 1995). Similar weapons, tactics, techniques and procedures are employed by police forces domestically in riot control, prisoner control, crowd control, refugee control, and self-defense, where the terminology of "less-than-lethal" is often used.
The Pentagon funds non-lethal weapons research for its Joint Non-Lethal Weapons Program (JNLWP). Proposed projects have included using intense electromagnetic fields to produce effects ranging from the disruption of short-term memory to total loss of control of voluntary bodily functions; directed energy weapons; genetically engineered microorganisms that would corrode roads and runways and produce targeted deterioration of metal parts, coatings and lubricants of weapons, vehicles and support equipment, as well as fuels and plastics. It is not clear how many of these ideas have actually been realized, but the group has already patented a microorganism that would decompose polyurethane, a common component of paint for ships and aircraft, including stealth anti-radar coatings.