Decapitation is the complete separation of the head (Latin: caput) from the body. Such an injury is fatal to humans and animals, since it deprives all other organs of the involuntary functions that are needed for the body to function, while the brain is deprived of oxygenated blood and blood pressure.

The term beheading refers to the act of deliberately decapitating a person, either as a means of murder or as an execution; it may be accomplished with an axe, a sword, or a knife, or by mechanical means such as a guillotine. An executioner who carries out executions by beheading is sometimes called a headsman. Accidental decapitation can be the result of an explosion, a car or industrial accident, improperly administered execution by hanging or other violent injury. Suicide by decapitation is rare but not unknown. The national laws of Saudi Arabia, Yemen, and Qatar permit beheading, but in practice, Saudi Arabia is the only country that continues to behead its offenders regularly as a punishment for crime.

Less commonly, decapitation can also refer to the removal of the head from a body that is already dead. This might be done to take the head as a trophy, for public display, to make the deceased more difficult to identify, for cryonics, or for other, more esoteric reasons.

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