A double agent is an operative of an intelligence, espionage, or similar agency or organization who is in fact secretly working for a rival group, most commonly the one aligned with the country or entity they had been assigned to spy on. Their "true" job as an agent of organization X requires them to act as an agent of organization Y, thus "double" agent. A double agent may infiltrate a rival agency with the original intention of secretly serving another, or may have begun as a normal agent "flipped" by his target by threats, compensation, or other methods of persuasion.

Double agents are useful in counterintelligence, as their awareness of the enemy's intelligence operation may allow them to identify and pass on information relating to operations in effect against their "true master". Further, the "enemy" with which they are actually affiliated may feed them information to pass on, this information often being false, unimportant, or obsolete and in any case worth less than whatever the "leak" expects to gain from the operation. In this way, the agent's handlers can help to further insinuate the agent into the rival's trust and power structure, pass on misinformation, or learn about the enemy by watching how it reacts when presented with a new piece of information.

Intelligence agencies, however, are nothing if not societies of distrust, and are continually performing operations with the aim of rooting out any double agents in their midsts. As such, double agents and their handlers must be cautious, even more so than the standard paranoia of your standard secret agent. Of course, if a man is willing to betray one agency to work for another, there is no reason to believe that he would not betray the second, and double agents might in fact be triple agents, adding another level of deceit. Of course, with each additional cycle of turnabout, the difficulty of maintaining cover increases, as does the mortality rate, and so such things tend to be rare.

Selected double agents of note:

Of course, due to the nature of spying, “double agent” status is often contested or unclear, and the very best double agents are not and will never be known as such.