Proceedings of the 18th international conference on World wide web

We are thrilled to have you attend this eighteenth edition of the WWW Conference series. The series started in 1994, at the CERN in Geneva, Switzerland. At the time, the Web was evolving at such a fast pace, like a newborn, that it held two meetings a year, and this until 1996. By then, in its toddler years, the conference found its rhythm and the Web research community started meeting on a yearly basis, typically around April or May. Today, we can say, continuing with our easy "child metaphor", that the conference is like a bright teenager, capable of wonders but with still a long way to go hopefully. This year we are happy to host WWW'2009 in Madrid, the charming capital of Spain. The technical program will hopefully meet and maybe even exceed your expectations, exposing the most recent progress in Web research across a variety of technical tracks. Indeed, we have this year a rich program with submissions originating from more than 50 countries, in a true world wide spirit. We reached a total of 105 accepted papers (including 2 alternate track papers) out of a total of 823 submissions, for an acceptance rate of under 13%. We thus maintained our selective standards as compared to previous years (with an acceptance rate of 12% for 103 accepted papers in 2008 and 15% for 111 accepted papers in 2007). Papers were submitted to 13 different tracks. In an effort to balance track sizes, we merged this year the previous "Browse and User Interfaces" and "Mobility" tracks into a unified "User Interfaces and Mobile Web" track. In addition, following the successful "geo driven" alternate "WWW in China" track of last year, a new "Web in IberoAmerica" track was offered this year. Its papers were subject to the same reviewing process. Overall, each track was coordinated by two to three vice-chairs and numerous Program Committee members, who worked hard on ensuring a fair reviewing process. Each paper was assigned to at least 3 reviewers and overviewed by at least one Vice-Chair. To ensure calibration between tracks, the Chairs and Vice-chairs of the Technical Program, as well as a few additional chairs, one of our general chair and one of next year program chair, attended a 2 day PC meeting on January 13-14, hosted by the Google Paris office. During these 2 days, all papers above a given threshold were discussed and calibrated across tracks in order to maximize quality. At the end of the two days, the team clustered papers into sessions, which crossed tracks when relevant.