"PGP (Pretty Good Privacy), as most Slashdot readers know, is one of the most popular 
software encryption programs ever. It is so good and so effective that in the early 1990s the FBI launched a multi-year investigation against Phil Zimmerman, the creator of PGP, for possible violation of federal export laws, especially ITAR (International Traffic in Arms Regulation). After many years of investigation, the FBI ultimately dropped its case against Zimmerman. Even though PGP is synonymous with end-user encryption, there have only been a few books written on the subject. Jump to 2006, and PGP & GPG: Email for the Practical Paranoid is a welcome title." Read the rest of Ben's review.
Source: http://slashdot.org/