in the algorithmic and foundational aspects, high-level approaches as well as more applied and technology-related issues regarding tools and applications of wireless sensor networks. June 2009 Jie Wu Viktor K. Prasanna Ivan Stojmenovic Message from the Program Chair This proceedings volume includes the accepted papers of the 5th International Conference on Distributed Computing in Sensor Systems. This year we int- duced some changes in the composition of the three tracks to increase cro- disciplinary interactions. The Algorithms track was enhanced to include topics pertaining to performance analysis and network optimization and renamed "- gorithms and Analysis. " The Systems and Applications tracks, previously s- arate, were combined into a single track. And a new track was introduced on "Signal Processing and Information Theory. " DCOSS 2009 received 116 submissions for the three tracks. After a thorough reviewprocess, inwhichatleastthreereviewsweresolicitedforallpapers, atotal of 26 papers were accepted. The research contributions in this proceedings span many aspects of sensor systems, including energy-e?cient mechanisms, tracking and surveillance, activity recognition, simulation, query optimization, network coding, localization, application development, data and code dissemination. Basedonthereviews, wealsoidenti?edthebestpaperfromeachtrack, which are as follows: BestpaperintheAlgorithmsandAnalysistrack: "E?cientSensorPlacement for Surveillance Problems" by Pankaj Agarwal, Esther Ezra and Shashidhara Ganjugunte. Best paper in the Applications and Systems track: "Optimal Allocation of Time-Resources for Multihypothesis Activity-Level Detection," by Gautam Thatte, ViktorRozgic, MingLi, SabyasachiGhosh, UrbashiMitra, ShriNarayanan, Murali Annavaram and Donna Spruijt-Metz. Best paper in the Signal Processing and Information Theory track: "D- tributed Computation of Likelihood Maps for Target Tracking" by Jonathan Gallagher, Randolph Moses and Emre Ertin.