Some 60 countries have currently enacted or proposed regulations for control of mycotoxins (primarily the aflatoxins) in food and animal feed. Various factors influence the establishment of limits for certain mycotoxins, but there is no consistent rationale for setting limits or for enforcement control. The enforcement of the regulations requires monitoring of suspected commodities. Many laboratories perform large numbers of determinations of mycotoxins, in particular aflatoxins, and consider their results to be reliable. Nevertheless, it often happens that laboratories find quite different analytical results on samples that have been especially homogenized for interlaboratory studies. The application of Quality Assurance principles contributes to the reliability of mycotoxin measurements. Quality Assurance is focused on the organizational process and the conditions under which laboratory studies are planned, performed, monitored, recorded, reported and archived. This is, in itself, an important contribution to the scientific value of a study. A Quality Assurance programme should include various elements, including (certified) reference materials, if available. Certified reference materials are stable, homogeneous products with certified values of the analyte(s) of interest. Various certified reference materials for mycotoxins have been prepared by the European Commission's Community Bureau of Reference, in co‐operation with several European laboratories (aflatoxin M1in milk powder, aflatoxins B1B2G1, and G2in peanut butter, aflatoxin B1in peanut meal and compound feed, deoxynivalenol in wheat and maize flour). Other reference materials are in a well‐advanced development stage (ochratoxin A in wheat flour and pig kidney, fumonisins B1and B2in maize).