BESC2021 will be a general topical conference with mainly invited talks by experts on recent progress in the theory and applications of ab initio study of quantum many-body effects in excited-state phenomena in materials, showcasing forefront research that involves advanced many-body approaches (e.g. GW, GW-BSE & beyond, DMFT, quantum Monte Carlo, TDDFT, TDGW, etc.) and new science in the excited state.