Contract killing is a form of murder or assassination in which one party hires another party to kill a targeted person or people. It involves an agreement which includes some form of compensation, monetary or otherwise. It is an illegal agreement. Either party may be a person, group, or organization. Contract killing has been associated with organized crime, government conspiracies, dictatorships, and vendettas. For example, in the United States, the Italian- and Jewish-American organized crime gang Murder, Inc. committed hundreds of murders on behalf of the National Crime Syndicate during the 1930s and '40s.

Murder is the unlawful killing of another human without justification or valid excuse committed with the necessary intention as defined by the law in a specific jurisdiction. This state of mind may, depending upon the jurisdiction, distinguish murder from other forms of unlawful homicide, such as manslaughter. Manslaughter is killing committed in the absence of malice, such as in the case of voluntary manslaughter brought about by reasonable provocation, or diminished capacity. Involuntary manslaughter, where it is recognized, is a killing that lacks all but the most attenuated guilty intent, recklessness.