CRISPR/Cas9 is a technique used to edit the genome of an organism. It involves using a specific enzyme, Cas9, which acts as a pair of molecular scissors to cut strands of DNA at specific points in the genome. The cuts allow for the insertion of new genetic material or the deletion or alteration of existing genetic material. The technique has been used to modify organisms such as plants, animals and bacteria, and can be used to create gene therapies that can treat diseases.