Shrouded in secrecy until very recently, Colossus was the world's first fully-functioning electronic computer, built during the Second World War and used at Bletchley Park to crack the codes of high-level Nazi communications. This book contains fascinating accounts of Colossus, of code-breaking, and of the extraordinary role played by the staff of Bletchley Park in WWII - including personal recollections by those who designed and built Colossus, recently declassified information, and historical essays considering its impact on the generations of computing technology that followed.