This book constitutes the thoroughly refereed post-conference proceedings of the Third International Conference on Mobile Computing, Applications, and Services (MobiCASE 2011) held in Los Angeles, CA, USA, during October 24-27, 2010. The 18 revised full papers presented together with 12 revised poster papers were carefully reviewed and selected from numerous submissions. The conference papers are organized in seven technical sessions, covering the topics of mobile pervasive applications, system issues, location-aware services, mobile phone based systems, mobile Web and services, tools for mobile environments, and mobile application development issues.