A murder–suicide is an act in which an individual kills one or more people either before or while killing themselves. The combination of murder and suicide can take various forms:

• Murder linked with suicide of a person with a homicidal ideation
• Murder which entails suicide, such as suicide bombing or the deliberate crash of a vehicle carrying the perpetrator and others
• Murder of an officer or bystander during the act of suicide by cop
• Suicide after murder to escape criminal punishment(s)
• Suicide after murder as a form of self-punishment due to guilt
• Suicide before or after murder by proxy
• Suicide after or during murder inflicted by others
• Murder to receive a death sentence willfully
• Joint suicide in the form of killing the other with consent, and then killing oneself

Suicide-lawful killing has three conceivable forms:

• To kill one's assailant through proportionate self-defense killing oneself in the process
• Lawful killing to prevent an individual from causing harm to others, in so doing killing oneself
• Lawful killing indirectly resulting in or contributing to suicide

Many spree killings have ended in suicide, such as in many school shootings. Some cases of religiously motivated suicides may also involve murder. All categorization amounts to forming somewhat arbitrary distinctions where relating to intention in the case of psychosis, where the intention(s) is/are more likely than not to be irrational. Ascertaining the legal intention (mens rea) is inapplicable to cases properly categorized as insanity.

Some use the term murder–suicide to refer to homicide–suicide, which can include manslaughter and is therefore more encompassing.