The Code Book by Simon Singh

This is an interesting discussion of codes and ciphers. The whole book is good, but the Mary Queen of Scots story, the Rosetta Stone story, and of course the ENIGMA story stand out. It has some of the best description of public key cryptography I have read. I can't say I understand the quantum crypto chapter, but probably mostly due to lack of interest. The hidden language chapter is very good and has a lot of linguistic relevance.