Hassell, Jonathan. RADIUS. Sebastopol, CA: O'Reilly & Associates, 2002. This is the book recommended by the FreeRADIUS team. In addition to the RADIUS protocol itself, this book covers FreeRADIUS in considerable depth.

Roser, Ken. “HOWTO: EAP-TLS Setup for FreeRADIUS and Windows XP Supplicant”: www.denobula.com. Mostly detailed procedure on configuring FreeRADIUS and Windows XP for WPA using EAP-TLS.

www.freeradius.org is the home page for the FreeRADIUS Project, where you can download the latest FreeRADIUS software and documentation.