This volume contains papers from the technical program of the 6th European Semantic Web Conference (ESWC 2009), held from May 31 to June 4, 2009, in Heraklion, Greece. ESWC 2009 presented the latest results in research and applications of Semantic Web technologies. In addition to the technical research track, ESWC 2009 featured a tutorial program, a PhD symposium, a system demo track, a poster track, a number of collocated workshops, and for the ?rst time in the series a Semantic Web in-use track exploring the bene?ts of applying Semantic Web technology in real-life applications and contexts. Thetechnical researchpaper trackreceivedover250submissions.The review process was organized using a two-tiered system, where each submission was reviewed by at least three members of the Program Committee. Vice Program CommitteeChairsorganizedadiscussionbetweenreviewers,collectedadditional reviews when necessary and provided a metareview for each submission. During a physical Program Committee meeting, the Vice Program Committee Chairs together with the Program Chairs selected 45 research papers to be presented at the conference.