Examines cryptography, discussing the history of the science, different cipher types, and how codes and codebreaking have changed with computers. Beginning with definitions of such basic terms as cryptanalysis, encryption, and decryption, this introduction from the Intelligence and Counterintelligence series emphasizes the point that cryptography is now a part of everyday business, not limited to espionage and the military. The narrative explains how various ciphers are constructed, from the simplest to the most complex, then covers basic concepts and types of cryptanalysis.