Abstract.  Cooperative peer-to-peer applications are designed to share the resources of each computer in an overlay network for the common good of everyone. However, users do not necessarily have an incentive to donate resources to the system if they can get the system's resources for free. This paper presents architectures for fair sharing of storage resources that are robust against collusions among nodes. We show how requiring nodes to publish auditable records of their usage can give nodes economic incentives to report their usage truthfully, and we present simulation results that show the communication overhead of auditing is small and scales well to large networks.