Manslaughter is the unlawful killing or homicide of a human being without the premeditation or malice (malice aforethought) required for the criminal offense of murder. Many states have two types of manslaughter: (1) voluntary manslaughter—the defendant intended to kill the victim, but did so in self-defense, or in the heat of passion and without premeditation, or the defendant was insane and did not understand that the killing was wrong; and (2) involuntary manslaughter—the defendant negligently or recklessly caused the death of another person—such as when a person is intoxicated while operating a motor vehicle and causes an accident that results in the death of another person.

Some states do not have separate criminal offenses for voluntary and involuntary manslaughter—these states may have the offense of manslaughter and identify certain aggravating factors that may enhance the penalties upon a conviction for manslaughter. Manslaughter is a felony offense and may be punished by a lengthy prison term. Manslaughter laws are generally located in a state's statutes—often in the penal or criminal code.

In California, manslaughter is categorized into voluntary and involuntary manslaughter, aligning with the general description provided. Voluntary manslaughter (California Penal Code 192(a)) occurs when a person kills another in the heat of passion or during a sudden quarrel without malice aforethought. It is treated as a felony and can result in a prison sentence of 3, 6, or 11 years. Involuntary manslaughter (California Penal Code 192(b)) involves unintentionally causing death through criminal negligence or during the commission of an unlawful act not amounting to a felony. This too is a felony, punishable by 2, 3, or 4 years in prison. Additionally, California recognizes vehicular manslaughter, where a death results from driving a vehicle in an unlawful way, with or without gross negligence, or while driving lawfully but in a manner likely to cause death. The penalties for manslaughter can be enhanced under certain circumstances, such as the use of a firearm or if the victim is a peace officer.