The authorized history of MI5 written by Christopher Andrew is titled "The Defence of the Realm: The Authorized History of MI5." This comprehensive book provides an in-depth account of the British Security Service, MI5, from its inception in 1909 through to the early 21st century. It covers various aspects of MI5's operations, including its role during both World Wars, the Cold War, and its adaptation to modern security challenges. Andrew was granted unprecedented access to MI5's archives, allowing him to present a detailed and authoritative narrative of the agency's history and its impact on national security.