A broad array of data is necessary to successfully complete the risk assessment. But in the real world, data sets are only as robust as their weakest link. In this guidance document on data requirements, you will learn about: • the impact of data gaps, small sample sizes, excessive variance in results, and generally poor data quality on the subsequent risk assessment and MRL derivation;• the types of data that are critical for completing the hazard, residue and exposure portions of a veterinary drug residue risk assessment; and• the specific characteristics of a drug compound that make residue assessments simpler or more challenging. This publication is part of the FAO JECFA Toolbox for Veterinary Drug Residue Risk Assessment. The toolbox provides practical guidance on the principles, modalities and technical requirements of JECFA in assessing the risks of veterinary drug residues in food and in recommending MRLs.