The concept of substantial equivalence was developed before any new genetically modified foods came to the market. Substantial equivalence is not a substitute for a safety assessment, but a part of the assessment process. As such, it provides a useful framework for regulatory scientists. Underlying the concept is the requirement that any safety assessment should show that a GM variety is as safe as its traditional counterparts, through a consideration of both intended and unintended effects. This involves consideration of a wide range of information, including agronomic properties, phenotypic changes and compositional data on key nutrients and toxicants.