The Puzzle Palace: Inside the National Security Agency, America's Most Secret Intelligence Organization

The National Security Agency (NSA) is a massive 30,000-person intelligence agency with unique origins (founded in 1952 by Harry Truman, through a unilateral directive) and a secretive history (it was not admitted to exist until 1975 and even today its operations are highly classified). James Bamford's 1982 book The Puzzle Palace was one of the first attempts to figure out what goes on behind its triple fence. The book is quite dated now but this is a very strong work of investigative journalism, as Bamford uncovers the NSA's role in Cold War spy craft and the surveillance of domestic antiwar protestors (among many other activities).