Since the beginning of recorded history, secrecy has been essential to the exercise of power, and secret messages - from military communications to financial transactions - are its stock in trade. The Encyclopedia of Cryptology explores the role of secret writing in many of history's decisive moments, such as the Teapot Dome scandal and the election of President Rutherford B. Hayes. It also traces the development of technologies from the fourth century B.C.E. to the present.