This International Standard gives guidelines for the quantitative compositional analysis of milk and liquid milk products, such as raw milk, processed milk, cream and whey, by measurement of the absorption of mid-infrared radiation. Additional built-in instrument features, such as a conductivity sensor, can improve the performance in the determination of compositional parameters and allow for the estimation of other parameters. The guidelines specified are applicable to the analysis of cow’s milk. The guidelines are also applicable to the analysis of milk of other species (goat, ewe, buffalo, etc.) and derived liquid milk products, provided adequate calibrations are generated for each application and adequate control procedures are in place. The application is limited to lower viscosity products that can be pumped through the flow system of the analyser and to analytes that do not result in optical saturation at the specific wavelengths being utilized.