This chapter describes the POSIX threads module and associated support for writing multithreaded kernels. At present, threads support is very new and not every combination of components is known to work; see Section 18.2 for a more detailed description of what has been tested. Section 18.3 describes the application program interface for the core POSIX threads module, while Section 18.4 contains a discussion of how the threads system interacts with the device driver framework.