A knife fight is a violent physical confrontation between two or more combatants in which one or more participants are armed with a knife. A knife fight is defined by the presence of a knife as a weapon and the violent intent of the combatants to kill or incapacitate each other; the participants may be completely untrained, self-taught, or trained in one or more formal or informal systems of knife fighting. Knife fights may involve the use of any type of knife, though certain knives, termed fighting knives, are purposely designed for such confrontations – the dagger being just one example.

A fighting knife has a blade designed to most effectively inflict injury in close-quarters physical confrontations. The combat knife and the trench knife are examples of military fighting knives.