Murder is the unlawful killing of another human without justification or valid excuse, especially the unlawful killing of another human with malice aforethought. This state of mind may, depending upon the jurisdiction, distinguish murder from other forms of unlawful homicide, such as manslaughter. Manslaughter is killing committed in the absence of malice, brought about by reasonable provocation, or diminished capacity. Involuntary manslaughter, where it is recognized, is a killing that lacks all but the most attenuated guilty intent, recklessness.

Most societies consider murder to be an extremely serious crime, and thus that a person convicted of murder should receive harsh punishments for the purposes of retribution, deterrence, rehabilitation, or incapacitation. In most countries, a person convicted of murder generally faces a long-term prison sentence, possibly a life sentence, and in a few, the death penalty may be imposed.