A key tool for any biologist today is the ability to edit the genome. CRISPR-Cas9 is an RNA-guided endonuclease that can be programmed to cut any gene in the genome. We have developed a simple protocol to repair Cas9-induced cuts using linear templates created by PCR. Our method can be used to edit the genome of human cells, mice and C. elegans. Genome editing is a technique that we use routinely in the lab, in particular to attach fluorescent tags to proteins so we can watch their dynamics live.