This volume contains the papers from the technical programmeof the 5th Eu- pean Semantic Web Conference, ESWC 2008, that took place during June 1-5, 2008 in Tenerife, Islas Canarias, Spain. ESWC 2008 was the latest in a series of annual, international events foc- ing on the dissemination and discussion of the latest research and applications of Semantic Web technologies. The call for papers saw over 270 submissions, a comparable ?gure to the previous year, indicating that the conference series has reached a certain level of maturity. The review process was organized - ing a two-tiered system. First, each submission was reviewed by at least three members of the ProgrammeCommittee. Submissions were also assignedto a - niorProgrammeCommitteemember, wholed discussionsbetweenreviewersand provided a metareview and provisional decision. A physical Programme C- mittee meeting was then held, where the ?nal decisions weremade. Competition was as strong as ever, and the Programme Committee selected 51 papers to be presented at the conference. In addition to the technical research paper track, a system demo track was included, withits ownreviewprocess. Twenty-?vedemo paperswereselectedfor publication. System demo authors were given the opportunity to present their workin dedicated sessionsduring the conference, while anevening receptionwas also devoted to the presentation of posters and demonstrations of systems. As in past years, ESWC subscribed to the call to "eat our own dog food," withthepublicationofarichsetofsemanticmetadatadescribingtheconference. Three invited talks were given by distinguished scientists: Nigel Shadbolt (Garlik Ltd.