Genome editing is the precise alteration of DNA in living cells by the cutting or removal of specific sequences, sometimes followed by insertion of new sequences at the cut site. CRISPR–Cas9 has become firmly established as the genome-editing method of choice, replacing the systems that had been developed and in use since the early 1990s. The CRISPR–Cas9 system has been developed from a mechanism used in prokaryotes as a defence against bacteriophage but actually functions in cells of all types of organisms. It is widely used in research as a gene knockout and editing tool; applications in veterinary medicine (such as increased resistance to disease) and human medicine (such as correction of disease-causing mutations) are under development. In agriculture and horticulture, the potential for various aspects of crop improvement is very large. Selected aspects of this potential are presented here, with particular focus on crop quality and disease resistance. The article ends with a brief discussion of the regulatory ‘environment’ in the USA and the EU.