The task of sizing droplets in sprays has confounded optical diagnosticians even though measurement techniques for sizing individual particles under laboratory conditions have been successfully developed. Difficulties with such measurement techniques result from incompatibilities between instru-mental capability and the physicochemical processes within sprays and the lack of standard practices for sampling of sprays, processing the associated data, and describing the results in precise terminology. An additional deficiency that hinders spray characterization is the lack of a calibration standard. Subcommittees of the American Society for Testing and Materials have undertaken activi-ties to relieve these shortcomings through the formulation of standards for the use of instrumentation, sampling, data processing, and terminology and the development of standard reference materials for calibration. Each of these tasks can profoundly affect the accuracy of spray measurement. Through partic-ipation in these task activities the optical engineer can become acquainted with the needs of the spray technologist. This interaction offers the hope that future measurement capability will possess both credibility and relevance to nonideal testing conditions.