To celebrate the 100th anniversary of the first administration of the tuberculosis vaccine BCG to a human being the Center for Infection and Immunity of Lille/Institut Pasteur de Lille organized the third international symposium on BCGFrom November 17 to 19, 2021. This international symposium gathered close to 200 delegates from all five continents to discuss BCG-related issues, ranging from the role of BCG today, the problem of BCG supply, to novel anti-tuberculosis vaccines and the effect of BCG on non-related effects. These non-specific, or off-target effects included the role of BCG in bladder cancer, in auto-immune and inflammatory diseases, as well as in all-cause mortality and heterologous infection, including COVID-19. For COVID-19 sanitary reasons, many delegates participated on-line, but more than 50 participants were physically at the institute. Overall, this symposium showed that, although 100 years old, BCG has still many secrets to be uncovered.