The second edition of the Guidance Document on the Definition of Residue incorporates feedback and insights gathered from users across OECD countries since the publication of the first edition. It provides a more detailed explanation of the ‘marker compound’ concept. In addition, examples have been added or updated to provide improved clarity for the Definition of the Residue selection. The harmonised Guidance for the Definition of Residue provides a common approach to residue identification of the pesticide and its metabolites and degradation products. Residue analysis for dietary risk assessment emphasizes analysis of the parent compound and its most significant metabolites and degradates, taking into consideration both exposure and relative toxicities.