Genome editing enables precise changes to be made in the genome of living cells. The technique was originally developed in the 1980’s but largely limited to use in mice. The discovery that a targeted double stranded break (DSB) at a unique site in the genome, close to the site to be changed, could substantially increase the efficiency of editing raised the possibility of using the technique in a broader range of animal models and potentially human cells. But the challenge was to identify reagents that could create targeted breaks at a unique genomic location with minimal off-target effects. In 2005, the demonstration that programmable zinc finger nucleases (ZFNs) could perform this task, led to a number of proof-of-concept studies, but a limitation was the ease with which effective ZFNs could be produced. In 2009, the development of TAL-effector nucleases (TALENs) increased the specificity of gene editing and the ease of design and production. However, it wasn’t until 2013 and the development of the CRISPR Cas9/guideRNA that gene editing became a research tool that any lab could use.