In 2020, Emmanuelle Charpentier and Jennifer Doudna were awarded the Nobel Prize for the development of a new technology for genome editing, CRISPR-Cas9. Before being a technological tool, CRISPR-Cas is an immune system used by bacteria to protect themselves against virus epidemics. The discovery of the CRISPR-Cas function was made by researchers trying to protect yoghurt-producing bacteria against viruses. Here, I propose to present 1) how CRISPR-Cas can effectively block virus epidemics, 2) how this knowledge has been used to develop various technological tools and 3) how we can hopefully use this understanding to fight pathogenic bacteria and protect friendly bacteria.