Scientists around the world have been making major improvements to CRISPR technology since its initial applications for genome engineering in 2012. (Check out our CRISPR 101 eBook for everything you need to know about CRISPR.) Like CRISPR, optogenetics has also been making headlines over the past decade. Optogenetics uses genetically encoded tools, such as microbial opsins, to control cellular activities using light. In 2015, scientists combined CRISPR and optogenetics techniques to develop a variety of photoactivatable CRISPR tools. These tools allow scientists to use light to externally control the location, timing, and reversibility of the genome editing process. Read on to learn about the various light-controlled CRISPR tools available to researchers - some readily found at Addgene.