Licence to kill is a literary device used in espionage fiction. It refers to the official sanction by a government or government agency to a particular operative or employee to initiate the use of lethal force in the delivery of their objectives. The initiation of lethal force is in comparison to the use of lethal force in self defence or the protection of life.
The idea of a licence to kill is popularly known from the James Bond novels and films, where it is signified by the "00" (double Oh) designation given to the agents in the series who are licensed to kill; Bond himself is famously agent 007.
In reality, the legitimacy of deadly force usage from country to country is generally controlled by statute law, particular and direct executive orders, the common law, or military rules of engagement.
In literary portrayals, the licence is presumed to be a discretionary one; distributed rarely and requiring extensive training to obtain, granted only to a handful of covert agents of a state in the interest of national security. The agent is not necessarily expected to kill enemies as part of a mission, but may receive immunity from prosecution (in his own country) if in the agent's estimation, this became necessary to complete it.