Officials say Section 702 is used to track foreign terrorists, hackers, weapons proliferators and hostile governments, and that it generates a significant portion of intelligence reported to the president.
A law that lets U.S. spy agencies tap into the emails, calls and online messages of foreigners abroad without getting a warrant for each target, as long as the goal is foreign intelligence.
Although the law targets foreigners, communications of Americans who interact with those foreigners can be swept up and later searched, raising Fourth Amendment questions for U.S. citizens.
Because the authority must be renewed periodically, each reauthorization gives Congress a chance to add or strip privacy safeguards, making the debate a regular flashpoint.
The attorney general and director of national intelligence certify categories of foreign intelligence targets, and agencies compel U.S. communications providers to hand over messages tied to specific selectors like email addresses.
When a targeted foreigner communicates with an American, that American's messages are also collected and stored in databases that agencies such as the FBI can later query.
The Foreign Intelligence Surveillance Court reviews the program's procedures annually, and inspector general audits track compliance, including improper U.S.-person queries.
A look at the foreign-intelligence surveillance law Congress periodically renews, and the debate over its impact on Americans' privacy.
Read the guide →Congress is again divided over whether to extend a foreign-intelligence surveillance authority that critics say sweeps in Americans' communications.
Read the brief →