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 Oregon, manslaughter is categorized into degrees and is defined under Oregon Revised Statutes (ORS) 163.118 and 163.125. Voluntary manslaughter is not specifically defined in Oregon; instead, the state recognizes 'Manslaughter in the First Degree' under ORS 163.118, which includes intentionally causing the death of another under circumstances that do not constitute murder because the defendant acted under extreme emotional disturbance. 'Manslaughter in the Second Degree' under ORS 163.125 covers situations where a person causes the death of another recklessly or with criminal negligence in cases involving a dependent person or a minor left in a vehicle. Both degrees of manslaughter are considered felonies, with the first degree carrying more severe penalties, including lengthy prison terms. Oregon law does not use the terms 'voluntary' or 'involuntary' manslaughter, but the statutes effectively distinguish between levels of culpability and circumstances surrounding the unlawful killing.