Model checking is a powerful technique for analyzing large, nite-state systems. In an in nite-state system, however, many basic properties are undecidable. In this paper, we present a new symbolic model checker which conservatively evaluates safety and liveness properties on in nite-state programs. We use Presburger formulas to symbolically encode a program's transition system, as well as its model-checking computations. All xpoint calculations are executed symbolically, and their convergence is guaranteed by using approximation techniques. We demonstrate the promise of this technology on some well-known in nite-state concurrency problems.