Reference samples of food materials with certified composition (e.g. bovine liver, skim milk powder) that serve as standards in analytical procedures. They validate laboratory methods, calibrate instruments and underpin proficiency testing, ensuring that food-analysis results are accurate and comparable between laboratories. Certified reference materials carry assigned values with stated uncertainties, produced under ISO 17034 by bodies such as NIST and the JRC; matrix-matched materials (e.g. infant formula powder) validate entire analytical procedures including extraction. Laboratories use them for method validation, quality-control charting and demonstrating competence in accreditation assessments.