This book constitutes the refereed proceedings of the 4th International Conference on Ad-Hoc Networks and Wireless, ADHOC-NOW 2005, held in Cancun, Mexico in October 2005. The 27 revised full papers presented together with the abstracts of 2 invited talks were carefully reviewed and selected from over 100 submissions. The papers discuss architectures, protocols, and algorithms for: access control, scheduling, ad hoc and sensor networks analytic methods and modelling for performance evaluation, characterization, optimization, auto-configuration, incentives and pricing, location awareness, discovery, dependence, and management, mesh networks, new applications, power management, power control, and energy-efficiency, quality-of-service, resource allocation, multimedia, routing (unicast, multicast, etc.), security and privacy, service discovery, systems and testbeds, wireless internet, and data management.