NSA warrantless surveillance (also commonly referred to as warrantless-wiretapping or -wiretaps) refers to the surveillance of persons within the United States, including United States citizens, during the collection of notionally foreign intelligence by the National Security Agency (NSA) as part of the Terrorist Surveillance Program. The NSA was authorized to monitor, without obtaining a FISA warrant, the phone calls, Internet activity, text messages and other communication involving any party believed by the NSA to be outside the U.S., even if the other end of the communication lay within the U.S.

Critics claimed that the program was an effort to silence critics of the Administration and its handling of several controversial issues. Under public pressure, the Administration allegedly ended the program in January 2007 and resumed seeking warrants from the Foreign Intelligence Surveillance Court (FISC). In 2008 Congress passed the FISA Amendments Act of 2008, which relaxed some of the original FISC requirements.

During the Barack Obama Administration, the U.S.Department of Justice continued to defend the warrantless surveillance program in court, arguing that a ruling on the merits would reveal state secrets. In April 2009 officials at the United States Department of Justice acknowledged that the NSA had engaged in overcollection of domestic communications in excess of the FISC's authority, but claimed that the acts were unintentional and had since been rectified.