United States Diplomatic Codes and Ciphers, 1775-1938 is the first basic reference work on American diplomatic cryptography. Weber's research in national and private archives in the Americas and Europe has uncovered more than one hundred codes and ciphers. Beginning with the American Revolution, these secret systems masked confidential diplomatic correspondence and reports.During the period between 1775 and 1938, both codes and ciphers were employed. Ciphers were frequently used for American diplomatic and military correspondence during the American Revolution. At that time, a system was popular among American statesmen whereby a common book, such as a specific dictionary,was used by two correspondents who encoded each word in a message with three numbers. In this system, the first number indicated the page of the book, the second the line in the book, and the third the position of the plain text word on that line counting from the left. Codes provided the most common secret language basis for the entire nineteenth century.Ralph Weber describes in eight chapters the development of American cryptographic practice. The codes and ciphers published in the text and appendix will enable historians and others to read secret State Department dispatches before 1876, and explain code designs after that year.