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 Missouri, manslaughter is categorized into two types: voluntary and involuntary manslaughter, as defined under Missouri Revised Statutes. Voluntary manslaughter, under Section 565.023, occurs when a person causes the death of another under a sudden passion arising from adequate cause, such as a provocation that would cause a reasonable person to lose self-control. Involuntary manslaughter, detailed in Section 565.024, can be of two degrees. First-degree involuntary manslaughter involves recklessness or criminal negligence that creates a substantial risk and ultimately leads to another person's death. Second-degree involuntary manslaughter is typically linked to acts of criminal negligence or when someone is killed during the commission of a non-felony unlawful act. Both types of manslaughter are considered felonies in Missouri, with potential penalties including imprisonment. The specific circumstances of the offense, such as the presence of aggravating factors, can influence the severity of the punishment upon conviction.