CRISPR (clustered regularly interspaced short palindromic repeats) is a prokaryotic immune surveillance system that is used by bacteria to recognize genetic material of infectious organisms, such as phage viruses. Using CRISPR-associated (Cas) proteins, this system cleaves foreign nucleic acid into fragments, thus defending the bacterium against the attacker. The 2020 Nobel Prize in Chemistry was awarded to CRISPR-Cas pioneers Emmanuelle Charpentier and Jennifer Doudna, who developed the CRISPR-Cas system to precisely edit genomic DNA. This technology has exploded at a breathtaking pace and is now used by almost every molecular biology laboratory around the world in a myriad of organisms. In this Virtual Issue, the FEBS Journal features articles reviewing the development of CRISPR/Cas9 technology and its applications to understand the functions of proteins in vivo.