This book constitutes the refereed proceedings of the Second International Conference on Mobile Ad-hoc and Sensor Networks, MSN 2006, held in Hong Kong, China in December 2006.The 73 revised full papers were carefully reviewed and selected from a total of 254 submissions. The papers address all current issues in mobile ad hoc and sensor networks and are organized in topical sections on routing, network protocols, security, energy efficiency, data processing, and deployment.