1 This paper presents a new approach to trusted Grid computing in a Peer-to-Peer (P2P) setting. Trust and security are essential to establish lasting working relationships among the peers. A P2P reputation system collects peer trust scores and aggregates them to yield a global reputation. We use a new trust overlay network (TON) to model the trust relationships among the peers. After analyzing the eBay transaction trace data, we discover a power-law distribution in user feedbacks. We develop a new reputation system, PowerTrust, to leverage power-law feedback characteristics. The PowerTrust system is built with locality-preserving hash functions and a lookahead random walk strategy. Dynamic system reconfiguration is enabled by the use of power nodes with well-established reputations. Through P2P simulation experiments on distributed file sharing and Grid parameter-sweeping applications (PSA), we demonstrate the PowerTrust advantages in fast reputation convergence and accurate ranking of...