Peer-to-Peer (P2P) systems rely on machine-to-machine ad-hoc communications to offer services to a community. Contrary to the classical client-server architecture, P2P systems consider all peers, i.e., all nodes participating in the network, as being equal. Hence, peers can at the same time act as clients consuming resources from the system, and as servers providing resources to the community. P2P applications function on top of existing routing infrastructures, typically on top of the IP network, and organize peers into logical and decentralized structures called overlay networks. In this column, we discuss exploratory research related to data management in P2P overlay networks. First, we discuss the notions of unstructured and structured P2P overlay networks. Then, we discuss data management in such networks by introducing an additional layer to handle semantic heterogeneity and data integration. Finally, we present a method based on sum-product message passing to detect inconsistent information in this setting.