This International Standard establishes principles for the measurement of droplet drift from all types of equipment designed for applying plant protection products. Detailed specifications relate to tractor-mounted, trailed and self-propelled agricultural sprayers operating in arable field crops (boom sprayers) and in bush and tree (including vines, hops, fruit) crops (including broadcast air-assisted sprayers). The principles are also applicable for any hand-held equipment or aircraft, but detailed protocols for such systems are not included in the specifications defined. All measurements are made with the sprayer operating outdoors in typical field conditions or over a defined surface including grass turf. Crop conditions include all arable (field) and horticultural crops that would be treated with a boom sprayer. Measurements of the crop and basic meteorological conditions at the time of spraying are made as part of the test procedure. This International Standard specifies the making of field measurements so as to determine the quantities of spray drift during application at defined distances from a treated area for risk assessment purposes. Standard measurement distances are defined that are used to enable the results from different experiments to be compared. Measures of drift can relate to either the deposition of spray onto horizontal surfaces outside of the treatment area or to airborne spray profiles that can be characterised at given downwind distances downwind of the treatment area. Deposition onto horizontal surfaces is relevant to the assessment of the risk of contamination of, for example, surface water; whereas the measurement of airborne profiles are relevant to risk assessments relating to inhalation effects and to the contamination of, for example, vegetative structures at field boundaries. This International Standard is applicable to both situations, although the emphasis in any series of trials may be varied by selection of the sampling matrix to be used. Where comparative assessments of the relative drift risk from different application systems are needed, then this International Standard is applicable, but some requirements relating to the use of reference spraying systems, collectors, selection and definition of the trial site may need to be modified. A description of such modifications is included, where appropriate. Drift measurements relate to application conditions aimed at achieving realistic levels of deposit on a target within the sprayed area. Since drift is commonly expressed as a proportion of the application rate, it is important that some direct assessments of target deposits be made as part of the drift measurement procedure.