This book is an overview of The Foreign Intelligence Surveillance Act (FISA), which was passed in 1978 and provides a statutory framework for the use of electronic surveillance in the context of foreign intelligence gathering. Congress sought to strike a delicate balance between national security interests and personal privacy rights. Subsequent legislation expanded federal laws dealing with foreign intelligence gathering to address physical searches, pen registers and trap and trace devices and access to certain business records. The Patriot Act of 2001 made significant changes to some of these provisions. In addressing international terrorism or espionage, the same factual situation may be the focus of both criminal investigations and foreign intelligence collection efforts. Some of these changes in FISA under these public laws are intended, in part, to facilitate information sharing between law enforcement and intelligence elements. In its Final Report, the 9/11 Commission noted that the removal of the pre-9/11 wall between intelligence and law enforcement has opened up new opportunities for co-operative action within the FBI .