We address the problem of highly transient populations in unstructured and loosely-structured peerto-peer systems. We propose a number of illustrative query-related strategies and organizational protocols that, by taking into consideration the expected session times of peers (their lifespans), yield systems with performance characteristics more resilient to the natural instability of their environments. We first demonstrate the benefits of lifespan-based organizational protocols in terms of end-application performance and in the context of dynamic and heterogeneous Internet environments. We do this using a number of currently adopted and proposed query-related strategies, including methods for query distribution, caching and replication. We then show, through trace-driven simulation and wide-area experimentation, the performance advantages of lifespan-based, query-related strategies when layered over currently employed and lifespanbased organizational protocols. While merely illustrative, the evaluated strategies and protocols clearly demonstrate the advantages of considering peers’ session time in designing widely-deployed peer-to-peer systems. 1. Introduction Due in part to the autonomous nature of peers, their architectural mutual dependency, and their excessively large populations, the transiency of peer populations (a.k.a. churn) and its implications on P2P systems have recently attracted the attention of the research community [3, 19, 7, 27, 16]. Measurement studies of deployed P2P systems have reported median session times1varying from one hour to one minute [29, 6, 27]. The implications of such a high degree of transiency on 1Where a node’s session time is the time from the node’s joining to its subsequent leaving from the system. We employthe overall system’s performance would clearly depend on the level of nodes’ investment in their neighboring peers. At the very least, the amount of maintenancerelated messages processed by