Software model checking tools based on a Counterexample Guided Abstraction Refinement (CEGAR) framework have attained considerable success in limited domains. However, scaling these approaches to larger programs with more complex data structures and initialization behavior has proven difficult. Explicit-state model checkers making use of states and operational semantics closely related to actual program execution have dealt with complex data types and semantic issues successfully, but do not deal as well with very large state spaces. This paper presents an approach to software model checking that actually executes the program in order to drive abstraction-refinement. The inputs required for the execution are derived from the abstract model. Driving the abstraction-refinement loop with a combination of constant-sized (and thus scalable) Boolean satisfiability-based simulation and actual program execution extends abstraction-based software model checking to a much wider array of programs than current tools can handle, in the case of programs containing errors. Experimental results from applying the CRunner tool, which implements execution-based refinement, to faulty and correct C programs demonstrate the practical utility of the idea.