When should a government provide a service inhouse and when should it contract out provision? We develop a model in which the provider can invest in improving the quality of service or reducing cost. If contracts are incomplete, the private provider has a stronger incentive to engage in both quality improvement and cost reduction than a government employee. However, the private contractor's incentive to engage in cost reduction is typically too strong because he ignores the adverse effect on non-contractible quality. The model is applied to understanding the costs and benefits of prison privatization.