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 New York, manslaughter is categorized into two degrees as defined in the New York Penal Law. First-degree manslaughter (Section 125.20) is similar to voluntary manslaughter and involves the intentional causing of death under certain mitigating circumstances, such as emotional disturbance. Second-degree manslaughter (Section 125.15) is akin to involuntary manslaughter and involves causing death due to reckless behavior. New York does not use the terms 'voluntary' or 'involuntary' manslaughter, but the concepts are embedded within these degrees. Manslaughter in New York is a felony offense, with first-degree manslaughter carrying a potential sentence of up to 25 years in prison, and second-degree manslaughter carrying a potential sentence of up to 15 years. The specific circumstances of the offense, such as whether the act was committed in a heat of passion or due to reckless behavior, will determine the degree of manslaughter and the associated penalties.