This book constitutes the proceedings of the 34th European Conference on IR Research, ECIR 2012, held in Barcelona, Spain, in April 2012. The 37 full papers, 28 poster papers and 7 demonstrations presented in this volume were carefully reviewed and selected from 167 submissions. The contributions are organized in sections named, query representation, blogs and online-community search, semi-structured retrieval, evaluation, applications, retrieval models, image and video retrieval, text and content classification, categorisation, clustering, systems efficiency, industry track, and posters.