After rapid initial growth in new starts, the expansion of the charter school movement has leveled off. This leveling is partly due to constraints in public policy -- as legislatures have imposed caps or other restrictions that make it difficult for more charter schools to form in some states. But the charter school movement also seems to be plateauing because of challenges of supply-- an apparent dearth of individuals and organizations with the willingness and capacity to start new schools. This paper discusses those supply challenges, what might be done about them, and what they mean for the prospects of expanded voucher programs. The next section explains the supply challenges in more detail. The following sections explore alternative paths to solving the new-school supply problem. The concluding section considers the implications of the discussion for voucher programs.