These proceedings contain the papers presented at the 4th International S- posium on Location and Context Awareness (LoCA) during May 7-8, 2009 in Tokyo,Japan.Locationandcontextawarenessarefundamentstonext-generation mobile and pervasive computing systems. Pervasive computing is a model of computing in which computation is everywhere and computer functions are - tegrated into everything. The ultimate aim is to make information, applications and services available anywhere and at anytime in the human environment in a ?uid manner appropriate to our current context. Once away from the desktop, we ?nd ourselves in a wide variety of contexts and hence situations. For computing to be relevant and useful in these emerging situations we must rely on a range of contextual cues. Context includes phys- logical, environmental, and computational data, whether sensed or inferred. In addition, context includes details of a user's activities, goals, abilities, pref- ences, a?ordances, and surroundings. With location and context awareness we can expect computers to deliver information, services, and entertainment in a way that maximizes convenience and minimizes intrusion.

This book constitutes the refereed proceedings of the 4th International Symposium on Location and Context Awareness, LoCA 2009, held in Tokyo, Japan, in May 2009.

The 18 revised full papers presented were carefully selected from 77 submissions. The papers describe original, previously unpublished research results, including new hardware platforms for sensing location and context, machine learning techniques for inferring user location and context from low-level sensor data, location and context representation, management, and distribution, and privacy policies and communication protocols for location and context information.