This volume contains the proceedings of the Third KES Symposium on Agent and Multi-agent Systems – Technologies and Applications (KES-AMSTA 2009)––held at Uppsala University in Sweden during June 3-5, 2009. The symposium was organized by Uppsala University, KES International and its Focus Group on Agent and Multi-agent Systems. The KES-AMSTA Symposium series is a sub-series of the KES Conference series. Following the successes of the First KES Symposium on Agent and Multi-agent Systems – Technologies and Applications (KES-AMSTA 2007), held in Wroclaw, Poland, from May 31 to 1 June 2007––and the Second KES Symposium on Agent and Multi-agent Systems – Technologies and Applications (KES-AMSTA 2008) held in Incheon, Korea, March 26-28, 2008––KES-AMSTA 2009 featured keynote talks, oral and poster presentations, and a number of workshops and invited sessions, closely aligned to the themes of the conference. The aim of the symposium was to provide an international forum for scientific - search into the technologies and applications of agent and multi-agent systems. Agent and multi-agent systems are an innovative type of modern software system and have long been recognized as a promising technology for constructing autonomous, c- plex and intelligent systems. A key development in the field of agent and multi-agent systems has been the specification of agent communication languages and formali- tion of ontologies. Agent communication languages are intended to provide standard declarative mechanisms for agents to communicate knowledge and make requests of each other, whereas ontologies are intended for conceptualization of the knowledge domain.