Shortly after the 9/11 terrorist attacks, Congress enacted the USA PATRIOT Act, in part, to provide enhanced investigative tools and to assist in the prevention of future terrorist activities and the preliminary acts and crimes which further such activities. To that end, the act eased restrictions on the government’s ability to collect information regarding people’s activities and conversations, both in domestic criminal investigations and in the realms of foreign intelligence gathering and national security. The changes are perceived by many to be necessary in light of the new breed of threats in a post 9/11 world. This book discusses the history of constitutional interpretations and legislative responses relevant to the collection of private information for criminal investigations, foreign intelligence gathering, and national security purposes.