Deadly force, also known as lethal force, is the use of force that is likely to cause serious bodily injury or death to another person. In most jurisdictions, the use of deadly force is justified only under conditions of extreme necessity as a last resort, when all lesser means have failed or cannot reasonably be employed.

The use of force, in the context of law enforcement, may be defined as the "amount of effort required by police to compel compliance by an unwilling subject".