The ideaIdeas of secret writing (cryptography), whether in terms of codesCode or ciphersCipher, has a long history. Written communication exhibits a number of phenomenaPhenomena with respect to the frequency of occurrence of letters of the alphabet in words. The aforementioned phenomena are true both for single letters and combinations of two letters (digraphs)Digraphs that appear in words. The science of cryptography seeks to suppress these phenomena in order to frustrate the cryptanalyst’sCryptanalyst efforts to convert secret writing back into clear text. The mechanism by which the ideaIdeas of secret writing has been realized evolved from manual to electro-mechanical operations. Perhaps the most famous cryptographic artifact used to mechanize the processProcess of encryption and decryption is the EnigmaEnigma machine, which is the subject of this chapter. We will reverse engineer the Enigma machineEnigma machine so the reader can see for themselves the mechanical and electrical mechanisms used by this portable, battery powered device. To make this exposition more understandable, extensive use will be made of annotated photographs of actual Enigma machinesEnigma machine, drawings from patents, drawings from instruction manuals, other visual aids, etc.