The book constitutes the refereed proceedings of the Third International Conference on Distributed Computing in Sensor Systems, DCOSS 2007, held in Sante Fe, NM, USA in June 2007.The 27 revised full papers presented were carefully reviewed and selected from 71 submissions. The papers class in three tracks covering the areas of algorithms, applications, and systems, thus bridging the gap between theory and practice and between the broader field of distributed computing and the specific issues arising in sensor networks and related systems.