An Efficient and Trustworthy P2P and Social Network Integrated File Sharing System Efficient and trustworthy file querying is important to the overall performance of peer-to-peer (P2P) file sharing systems. Emerging methods are beginning to address this challenge by exploiting online socialnetworks (OSNs). However, current OSN-based methods simply cluster common-interest nodes for high efficiency or limit the interaction between social friends for high trustworthiness, which provides limited enhancement or contradicts the open and free service goal of P2P systems. Little research has been undertaken to fully and cooperatively leverage OSNs with integrated consideration of proximity and interest. In this work, we analyze a BitTorrent file sharing trace, which proves the necessity of proximity- and interest-aware clustering. Based on the trace study and OSN properties, we propose a social network integrated P2P file sharing system with enhanced efficiency and trustworthiness (SOCNET) to fully and cooperatively leverage the common-interest, proximity-close, and trust properties of OSN friends. SOCNET uses a hierarchical distributed hash table (DHT) to cluster common-interest nodes, then further cluster proximity-close nodes into a subcluster, and connects the nodes in a subcluster with social links. Thus, when queries travel along trustable social links, they also gain higher probability of being successfully resolved by proximity-close nodes, and it simultaneously enhances efficiency and trustworthiness. We further propose different strategies to guide nodes toforward a file query to friends that are more trustworthy and more likely to resolve the queries or forward the query to file holders. We also propose follower- and cluster-based file replication algorithmsto enhance file search efficiency. The results of trace-driven experiments on the real-world PlanetLab testbed demonstrate the higher efficiency, trustworthiness, and dynamism-resilience of SOCNET compared with other systems. Experimental results also confirm the effectiveness of the pro- osed strategies to improve SOCNET’s performance.