History teaches that government spying is naturally subject to abuse without strong oversight, yet only the tiniest fraction of electronic surveillance of Americans — the tip of a vast and rapidly growing iceberg — is meaningfully visible to Congress, let alone the general public. Under the controversial FISA (Foreign Intelligence Surveillance Act) Amendments Act of 2008, set to expire at the end of the year, the National Security Agency is empowered to vacuum up the international communications of Americans under sweeping authorizations that dispense with the need for individual warrants. Despite reports of large-scale overcollection of Americans’ e-mails and phone calls, including purely domestic traffic, the NSA has brazenly refused to give Congress any estimate of how many citizens’ private conversations are being captured in its vast databases, and legislators have shown little willingness to demand greater transparency as they prepare to reauthorize the law. Increasingly, even ordinary criminal investigations employ off-the-books electronic surveillance techniques that circumvent federal reporting requirements. The public is informed about the few thousand wiretaps authorized every year but remains largely in the dark about newer and far more prevalent techniques, such as the routine use of cell phones as sophisticated tracking devices.