CRISPR/Cas is a microbial adaptive immune system that uses RNA-guided nucleases to cleave foreign genetic elements. The CRISPR/Cas9 method has been engineered from the type II prokaryotic CRISPR system and uses a single-guide RNA to target the Cas9 nuclease to a specific genomic sequence. Cas9 induces double-stranded DNA breaks which are repaired either by imperfect non-homologous end joining to generate insertions or deletions (indels) or, if a repair template is provided, by homology-directed repair. Due to its specificity, simplicity and versatility, the CRISPR/Cas9 system has recently emerged as a powerful tool for genome engineering in various species. This technology can be used to investigate the function of a gene of interest or to correct gene mutations in cells via genome editing, paving the way for future gene therapy approaches. Improvements to the efficiency of CRISPR repair, in particular to increase the rate of gene correction and to reduce undesired off-target effects, and the development of more effective delivery methods will be required for its broad therapeutic application.