The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a space mission concept currently under Phase A study by the European Space Agency (ESA) as candidate M5 mission, in view of a launch opportunity in 2032 (now cancelled by ESA). Within this dedicated scientific conference, the THESEUS science case will be presented through dedicated review talks, discussing the status-of-the-art knowledge on GRB science, early Universe studies, gravitation wave physics, and transient Universe phenomena in general. The development status of the instruments on-board THESEUS will be reported and discussed, together with the current assumptions for the mission profile. Contributed talks are expected to enrich the program and suggest further exploitations of the THESEUS instrumentation in many other fields of the modern Astronomy, Astrophysics, Cosmology, and fundamental physics. Through this conference, we aim at strengthening the involvement of the community in the project and boost even more the synergies being developed between THESEUS and all other facilities operational in the 2030s in the multi-wavelength domains.

Carried out during 23-26 March 2021 (moved to virtual due to the pandemics). The conference was followed by 478 attendees.