In the spy game, if you can listen, you can learn, and gaining that crucial ability to eavesdrop has required some deeply creative ingenuity.

For some covert missions, the goal is not information, but assassination, and lethal toxins have been deployed by spy agencies to kill perceived foes.

As long as there has been espionage, sex and the promise of it have been powerful tools of persuasion and blackmail — practices that continue today.

Methods for covertly capturing sensitive data have grown infinitely more advanced as the devices used to do so have become exponentially smaller.

From old-school "dead drops" to high-tech digital transfers: Learn how intelligence officers actually acquire the information collected by sources.

Encryption is a key tool for keeping valuable information secret — but some ingenious minds have managed to crack seemingly impenetrable codes.

What leads someone to spy against their own nation? Motivations vary but tend to fall into one of four categories, as notorious cases demonstrate.