This paper describes a scheduling abstraction, called group scheduling, that emphasizes fine grain configurability of system scheduling semantics. The group scheduling approach described and evaluated in this paper provides an extremely flexible framework within which a wide range of scheduling semantics can be expressed, including familiar priority and deadline based algorithms. The paper describes both OS and middleware based implementations of the framework, and shows through evaluation that they can produce the same behavior for a non-trivial set of application computations. We also show that the framework can support application-specific scheduling constraints such as progress, to improve performance of applications whose scheduling semantics do not match those of traditional scheduling algorithms.