The Enigma code machine was used extensively by German armed forces in WWII. To counter its use, the British developed a massive codebreaking project which successfully captured and decoded huge numbers of German messages. This effort was so secret that information about the Enigma and the codebreaking did not reach the public until the 1970's. Since then the general interest in the Enigma and the codebreaking has steadily increased. This book concisely discusses the Enigma design and use and shows functional data flows through the system. Some discussion of British codebreaking is included. To develop his own understanding , the author wrote a computer simulator of the Enigma and the source code is included in the book.