Policymakers have shown increasing interest in replicating high-quality education models as a way to improve chronically underperforming schools. Charter management organizations (CMOs) have been touted as one organizational model poised to be such a vehicle for reform. CMOs are nonprofit organizations that operate a network of charter schools with a common mission or instructional design and shared central office support. In this article, the authors describe the theory of action behind CMOs and their emergence onto the education reform scene, finding promising signs that, as a network of schools, CMOs have more leverage than individual charter schools, and yet more nimbleness than traditional school districts, to replicate "what works." Using data collected from a national study of 25 CMOs engaging in scale-up, the authors investigate the essential elements for CMO growth, identifying the influences of federal, state, and local policies, as well as internal organizational capacities, that either restrict or facilitate CMO expansion. (Contains 1 table, 2 figures and 5 notes.)