Homicide is the act of one person causing the death of another person. Not all homicides are murder—some are manslaughter due to mitigating circumstances—and some are lawful when justified by an affirmative defense such as self-defense or insanity.

Criminal homicide generally involves (1) intent to cause death or serious bodily injury, or (2) negligence that causes the death of another person. Criminal homicide committed with the intent to cause death or serious bodily injury is generally charged as the criminal offense of murder (committed with intent and with premeditation or malice) or as voluntary manslaughter or second degree murder (committed with intent but without premeditation or malice).

And criminal homicide caused by negligence is generally charged as the criminal offense of involuntary manslaughter—for example, when a person is driving recklessly or speeding and hits another motor vehicle or pedestrian, causing the death of the other motorist or the pedestrian. A person driving a motor vehicle while intoxicated by drugs or alcohol who hits another motor vehicle or pedestrian, causing the death of the other motorist or the pedestrian, may be charged with involuntary manslaughter, or with a more specific offense like intoxication manslaughter or vehicular homicide—depending on applicable state laws.

Criminal homicide laws vary from state to state—including the names, degrees of severity, and punishments. These laws are generally found in a state’s statutes—often in the penal or criminal code.

In Montana, homicide is defined as the act of one person causing the death of another. Not all homicides are considered murder; some may be classified as manslaughter, which includes instances where mitigating circumstances are present, or they may be justified by affirmative defenses such as self-defense or insanity. In Montana, deliberate homicide, which involves intent to cause death or serious bodily injury, is charged as murder and requires premeditation or malice. When the intent is present but without premeditation or malice, the charge may be mitigated to deliberate homicide or mitigated deliberate homicide, which is similar to voluntary manslaughter or second-degree murder in other jurisdictions. Negligent homicide, on the other hand, occurs when a person's negligence leads to the death of another, such as in cases of reckless driving or driving under the influence of drugs or alcohol. In such cases, the charge in Montana may be negligent homicide, which is akin to involuntary manslaughter, intoxication manslaughter, or vehicular homicide in other states. The specific charges and penalties for criminal homicide are outlined in Montana's statutes, particularly in the Montana Code Annotated (MCA), which includes the state's penal or criminal code.