In a world that is increasingly unstable, intelligence services like the American CIA and the United Kingdom's MI6 exist to deliver security. Whether the challenge involves terrorism, cyber-security, or the renewed specter of great power conflict, intelligence agencies mitigate threats and provide decisional advantage to national leaders. But empowered intelligence services require adequate supervision and oversight, which must be about more than the narrow (if still precarious) task of ensuring the legality of covert operations and surveillance activities.

Global Intelligence...