National Cryptologic Museum
The National Cryptologic Museum has several exhibits online.

Beginner's Guide to Cryptography
An introduction to cryptography.

CRYPTOLOGIA
A quarterly journal devoted to all aspects of cryptology.

CRYPTOGRAPHY.COM
This site is run by Paul Kocher and provides information about secure communications.

Secret Code Breaker Online
Excerpts from the Secret Code Breaker series of publications.

Spy letters of the American Revolution
A collection of documents at the University of
Michigan.

Decoding Nazi Secrets
The companion web site to the NOVA PBS special, Decoding Nazi Secrets.

The Secret Language
Information on substitution and transposition ciphers at San Francisco's Exploratorium web site.

Navajo Code Talkers
A site dedicated to the Navajo code talkers who served in the United States military in World War II.