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 Pennsylvania, manslaughter is categorized into two types: voluntary and involuntary manslaughter, as defined under the Pennsylvania Consolidated Statutes. Voluntary manslaughter (18 Pa.C.S. § 2503) occurs when a person kills another without lawful justification if, at the time of the killing, the actor is acting under a sudden and intense passion resulting from serious provocation by the individual killed. Involuntary manslaughter (18 Pa.C.S. § 2504) occurs when a person causes the death of another person as a result of reckless or grossly negligent behavior, such as a fatal accident caused by drunk driving. Manslaughter in Pennsylvania is considered a felony offense, with voluntary manslaughter typically treated as a felony of the first degree and involuntary manslaughter as a misdemeanor of the first degree or a felony of the second degree, depending on the circumstances and the age of the victim. The penalties for manslaughter can include substantial prison time, with the specific sentence depending on factors such as the nature of the offense and the defendant's criminal history.