For the past two years, the FreeBSD Project has been performing incremental point releases against its RELENG_4 -STABLE branch, producing FreeBSD 4.0 through FreeBSD 4.7. Since the release of FreeBSD 4.0, the FreeBSD Project has also been working on FreeBSD 5.0-CURRENT, an active branch in which far more aggressive and long term development has occurred. Features found in the branch include a re-design of the kernel to support a multi-threaded kernel operating on multiple processors concurrently, scheduler activations to support highly scalable userland threading through asynchronous system calls, support for pluggable kernel security modules and mandatory access control, a new revision of the UFS file system, and much more. This talk will discussion both the specific features in FreeBSD 5.0, and the challenges in the development process that lead to a one year delay in its release. In addition, it will describe some of the changes in the FreeBSD development process that were required to support several large and concurrent kernel development projects.