These proceedings contain the papers presented at ECIR 2009, the 31st - ropean Conference on Information Retrieval. The conference was organized by the Institut de Recherche en Informatique de Toulouse (IRIT), in cooperation with the Information Retrieval Specialist Group of the British Computer So- ety (BCS-IRSG) and was supported by the Special Interest Group on Infor- tion Retrieval (ACM SIGIR), the French Association of Information Retrieval (ARIA) and E-IRSG. It was held during April 6-9, 2007 in Toulouse, hosted by the Pierre Baudis congress center. ECIR 2009 con?rmed the growth trend of submissions, with 188 full-paper submissions. Many of these submissions came from outside Europe, and 25 countries were represented in the ?nal ECIR 2009 program, re?ecting the international po- larityandreputationoftheconferenceseries.Furthermorethetraditionalstrong focus on students was well preserved, with their participation being great. All submitted papers were reviewed by at least three members of the int- national Program Committee. Out of the 188 papers 42 were selected as full research papers and a further 18 were accepted as short research papers. Short papers were given 8 pages in the proceedings (instead of 12). Out of these 60 selected papers, 30 have a student as the primary author. The accepted papers themselves come from a mixture of universities, researchinstitutes and comm- cial organizations. There was also a separate call for posters. Each of the 60 poster submissions wasreviewedbythreeProgramCommitteemembers, aswithpapersubmissions. Twenty-?ve posters were accepted for presentation. Takentogether, thesepaperscoverthestateoftheartininformationretrieval, including topicssuchasretrievalmodels, evaluationandWeb search, andeme- ing topics such as learning to rank, expert search and opinion detect