Kerberos: The Network Authentication Protocol
Reference distribution and official documentation for Kerberos. Software is subject to US export control. (MIT)

Kerberos Network Authentication Service
A resource site with documentation, papers and software distributions. Software may be subject to US export control.

Kerberos Reference Page
An index of related resources. Includes software distributions and patches, as well as user documentation.

Heimdal
An international free implementation. Includes downloads, distribution information and mailing list contacts.

RFC 1510
An overview and specification of the official internet protocol.

Cybersafe Ltd
Provides products for database security, web security, and security infrastructure based on the Kerberos protocol, and also provides Kerberos consulting and support.

CERT Advisory: Buffer Overflow in Kerberos Administration Daemon
"Multiple Kerberos distributions contain a remotely exploitable buffer overflow in the Kerberos administration daemon. A remote attacker could exploit this vulnerability to gain root privileges on a vulnerable system."

Kerberos: An Authentication Service for Computer Networks
A technical paper documenting the system and standard. Includes diagrams and references.

How to Kerberize your Site
Excellent tutorial on implementation. Contains detailed steps to follow for a successful installation, as well as answers to common questions.

Kerberos Infrastructure HowTo
A step-by-step description of the design and configuration of a GNU/Linux Kerberos infrastructure.

Notes on Integrating Windows, RedHat, and HPUX Using Kerberos
Brief tutorial on configuring *nix systems to authenticate off a Microsoft Active Directory server.

GNU Shishi
Freely available implementation of Kerberos 5. Includes system documentation and downloads.

Kerberos FAQ
Answers to frequently asked questions.