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 Mexico, manslaughter is categorized as either voluntary or involuntary, aligning with the general distinction made in many states. Voluntary manslaughter in New Mexico occurs when someone kills another in a sudden quarrel or in the heat of passion, without premeditation. Involuntary manslaughter, on the other hand, happens when a person's unlawful act negligently causes the death of another, or when a lawful act is committed in a negligent manner, resulting in death. This could include cases where a person is killed as a result of someone's reckless driving. Both types of manslaughter are considered third-degree felonies under New Mexico law, as outlined in the New Mexico Statutes Annotated (NMSA) 1978, Section 30-2-3. The penalties for manslaughter can include imprisonment and fines, with the potential for increased sentences if aggravating factors are present. It's important to note that the specific circumstances of a case can greatly affect the charges and penalties, and an attorney can provide more detailed information based on the facts of a particular case.