We have established a bacterial artificial chromosome (BAC)-based RG system to generate recombinant severe acute respiratory syndrome coronavirus 2 (rSARS-CoV-2) and to engineer reporter-expressing recombinant viruses to assess viral infection in vitro and in vivo . To date, we have shared our BAC-based RG system with more than 100 laboratories around the world, which has helped to expedite investigations with SARS-CoV-2.