This book constitutes the refereed proceedings of the 39th European Conference on IR Research, ECIR 2017, held in Aberdeen, UK, in April 2017.  The 36 full papers and 47 poster papers presented together with 5 Abstracts, were carefully reviewed and selected from 248 submissions. Being the premier European forum for the presentation of new research results in the field of Information Retrieval, ECIR features a wide range of topics such as: IR Theory and Practice; Deep Learning and IR; Web and Social Media IR; User Aspects; IR System Architectures; Content Representation and Processing; Evaluation; Multimedia and Cross-Media IR; Applications.