The need for more and better manpower information is hampered by the lack of adequate occupational data classification systems. The diversity of interests in occupations probably accounts for the absence of consensus regarding either the general outlines or the specific details of a standardized occupational classification system which would reduce the cost of generating data and enhance communication. Neither extreme accuracy nor precise detail are necessary but a system of classification based on principles is essential. Existing classification systems reviewed are the socio-economic, worker traits, and curriculum areas types. "Function" as a underlying principle has conceptual, operational, and analytical advantages which are described in detail. (MS)