The Fair Share Scheduler (FSS) is a process scheduling scheme within the UNIX™ operating system that controls the distribution of resources to sets of related processes. This control offers features that are useful to many applications, including user control of service level, execution predictability, fair resource allocation, predictable and fair billing, and load insulation between user communities. This paper discusses the concepts of a fair share scheduler, the motivation for and history behind FSS, some practical FSS applications, the user and administrator interfaces to FSS, and the design philosophy of FSS.