This book constitutes the proceedings of the Third International Conference of the CLEF Initiative, CLEF 2012, held in Rome, Italy, in September 2012. The 14 papers and 3 poster abstracts presented were carefully reviewed and selected for inclusion in this volume. Furthermore, the books contains 2 keynote papers. The papers are organized in topical sections named, benchmarking and evaluation initiatives, information access, and evaluation methodologies and infrastructure.