The Spy Who Came In from the Cold Spying, as the cliché has it, is the world’s second-oldest profession,2 yet a profusion of state practice has been tempered by the regular denunciation of intelligence gathering, expulsion or execution of agents, and sporadic demands for nonrepetition of such activities.3 This is due in part to the nonreflexive manner in which governments approach the subject: we and our friends merely gather information; you and your type violate sovereignty. Most domestic legal systems thus seek to prohibit intelligence gathering by foreign agents while protecting the state’s own capacity to conduct such activities abroad. What, then—if anything—does international law have to say about the subject? A surprising amount, though the surprise comes largely from the fact that the issue tends to be approached indirectly: intelligence is less a lacuna in the legal order than it is the elephant in the room.