This book constitutes the thoroughly refereed post-conference proceedings of the Third International ICST Conference Mobile Lightweight Wireless Systems (MOBILIGHT 2011) held in Bilbao, Spain on May 9-10. 2011. In numbers, MOBILIGHT 2011 was organized as a 2-day single-track event with 18 technical presentations, and 3 specialized workshops focused on opportunistic sensing and processing in mobile wireless sensor and cellular networks (MOBISENSE), multimode wireless access networks (MOWAN) and strategic network planning applied to market regulation (NETSTRAT), totaling to 34 papers presented during the conference and included in the proceedings