NSA warrantless surveillance — also commonly referred to as "warrantless-wiretapping" or "-wiretaps" — refers to the surveillance of persons within the United States, including U.S. citizens, during the collection of notionally foreign intelligence by the National Security Agency (NSA) as part of the Terrorist Surveillance Program. In late 2001, the NSA was authorized to monitor, without obtaining a FISA warrant, phone calls, Internet activities, text messages and other forms of communication involving any party believed by the NSA to be outside the U.S., even if the other end of the communication lays within the U.S.

Critics claimed that the program was an effort to silence critics of the Bush 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 Obama administration, the U.S. Department of Justice (DOJ) 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 DOJ 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.