People throughout history have written messages in code and ciphers to pass along closely held, secret information. Today, countries around the world enlist cryptanalysts to intercept and crack messages to keep our world safe. The book explores many aspects of cryptology, including famous people who used and invented codes and ciphers, such as Julius Caesar and Thomas Jefferson; codes used during wars, including the Enigma machine, whose cracking helped the Allies gather critical information on German intelligence in World War II; and work currently being done by the government, such as in the National Security Agency. Readers also will learn about unsolved codes and ciphers throughout history, little-known codes used today, and devices used over the years by governments and their spies to conceal information. This book includes hands-on activities that allow kids to replicate early code devices, learn several different codes and ciphers to encode and decode messages, and hide a secret message inside a hollow egg.