Starting with Version 3.0, XSB supports the use of POSIX threads to perform separable computations, and in certain cases to parallelize them. POSIX threads have a simple and clear API, and are available on all Unixes and, by using open-source libraries, on Windows as well (see Section 7.6 to configure under Windows). This chapter introduces how to program with threads in XSB through a series of examples. Later sections discuss performance aspects of our implementation as well as describing relevant predicates. A general knowledge of multi-threaded programming is assumed, such as can be found in [39,8].