ECIR 2021, the 43rd edition of the annual BCS-IRSG European Conference on Information Retrieval, initially planned to be a in-person conference in Lucca, due to COVID-19 concerns will be held entirely online from March 28 to April 1, 2021. The ECIR conference is the premier European forum for the presentation of new research results in the broadly conceived area of Information Retrieval (IR), and has a strong focus on the active participation of early-career researchers. The General Chairs of ECIR 2021 invite researchers, academics, students, and industry leaders working in the field to join us online for a rich program featuring full-paper and poster presentations, system demonstrations, tutorials, workshops, an industry-oriented event, and great social events.