This paper presents lottery scheduling, a novel randomized resource allocation mechanism. Lottery scheduling provides ef- ficient, responsive control over the relative execution rates of computations. Such control is beyond the capabilities of conven- tional schedulers, and is desirable in systems that service requests of varying importance, such as databases, media-based applica- tions, and networks. Lottery scheduling also supports modular resource management by enabling concurrent modules to insulate their resource allocation policies from one another. A currency ab- straction is introduced to flexibly name, share, and protect resource rights. We also show that lottery scheduling can be generalized to manage many diverse resources, such as I/O bandwidth, mem- ory, and access to locks. We have implemented a prototype lottery scheduler for the Mach 3.0 microkernel, and found that it provides flexible and responsive control over the relative execution rates of a wide range of applications. The overhead imposed by our unoptimized prototype is comparable to that of the standard Mach timesharing policy.