This book constitutes the refereed proceedings of the 12 European Conference on Wireless Sensor Networks, EWSN 2015, held in Porto, Portugal, in February 2015. The 14 full papers and 9 short papers presented were carefully reviewed and selected from 85 submissions. They cover a wide range of topics grouped into five sessions: services and applications, mobility and delay-tolerance, routing and data dissemination, and human-centric sensing.