The ESERA 2021 Online Conference will be organised by the University of Minho (Braga, Portugal) from 30 August to 3 September 2021. The WebApp will be the new conference venue and adjustments to the scientific programme will be made in order to adapt to the new online format as well as to create an interactive participant experience. The conference programme will, as usual, include invited plenary sessions, single paper presentation sessions, symposia as well as workshops. Posters will also be made available in an interactive online format. These presentation formats are similar to previous face-to-face ESERA Conferences, but the preparation and the interactive presentations will be different. Presenters of single papers, symposia and workshops are requested to record their presentation and send them to the conference secretariat until the deadline, which will be informed well in advance. Recorded presentations will be uploaded to the Conference Programme before the conference dates allowing registered participants to consult the presentations online in advance. Conference sessions are organised in Strands in the online Conference Programme. Single paper sessions and Symposia will also include real-time moderated interactive Q&A between assisting participants and the presenters. As a large number are expected to assist the sessions, participants are encouraged to write their questions online. Questions can be directed publicly (visible for all participants, the moderator and the author) or in a private message to the author/presenter. The session moderator will place a selection of the public questions, submitted in writing before and during the session, in a live interaction with the presenters who will be present online to respond in real-time. The live Q&A session will take place at the end of each session.