LinuxKernel > SELinux
Security-Enhanced Linux (SELinux) is a project to implement mandatory access control under Linux. This project was initially developed by the National Security Agency (NSA), as a reference implementation.
Debian SELinux support
The Debian packaged Linux kernels have SELinux support compiled in, but disabled by default. To enable it, see the Setup Notes.
Setup - How to setup your Debian system to use SELinux
Issues - Issues currently affecting SELinux support
Notes - Scratch space with some notes about SELinux use and setup
Please note that SELinux is a Linux-specific feature and Debian packages shouldn't assume it is present (unless they're Linux-specific packages for some reason). Note for developers: Remember to check whether this is a Linux platform by using dpkg-architecture variables in debian/rules, and conditionalise the libselinux Build-Dependency using  tags. Something like [linux-any] should be fine.
There is a mailing list about SELinux development in Debian hosted on alioth. Use the selinux-devel Mailman page to subscribe to the list or browse the archives. As we don't have a user list you can ask questions on usage there.
For general SELinux questions and discussion #selinux on chat.freenode.net
Security-Enhanced Linux - Documentation - Red Hat -- this is probably the best documentation on SELinux available and almost all of it also applies to Debian.
SELinux Project Wiki -- "the official Security Enhanced Linux (SELinux) project page"