This book constitutes the thoroughly refereed post-conference proceedings of the First International Workshop on Citizen Sensor Networks, CitiSens 2012, in Montpellier, France, on August 27, 2012. The 7 revised full papers presented together with 1 keynote lectures were carefully reviewed and selected from 16 submissions. The accepted papers deal with topics like crowdsourcing, smart cities, multi-agent systems, privacy in social networks, data anonymity or smart sensors.