This book constitutes the refereed proceedings of the Third International Conference on Semantics and Digital Media Technologies, SAMT 2008, held in Koblenz, Germany, in December 2008. The 12 revised full papers presented together with the abstracts of 2 invited keynote lectures were carefully reviewd and selected from 52 submissions. The conference brings together forums, projects, institutions and individuals investigating the integration of knowledge, semantics and low-level multimedia processing, including new emerging media and application areas. The papers cover topics such as semantic analysis and multimedia, semantic retrieval and multimedia, semantic metadata management of multimedia, semantic user interfaces for multimedia, semantics in visualization and computer graphics, as well as applications of semantic multimedia.