Two mRNA vaccines, which received emergency authorization in late 2020, have proven critical in the fight against COVID-19. These vaccines, the first of their kind, were the culmination of decades of research on RNA. Delivered as strands of mRNA that encode a viral protein, the vaccines enter cells and begin producing proteins, allowing the immune system to recognize the virus if encountered later. Following the success of COVID-19 vaccines, researchers hope that mRNA vaccines and therapies will prove useful against many other diseases.