This document studies the changes in the total number of holders of bachelor's and more advance degrees from 1930 to 1971 and provides detailed annual estimates of degree holders in 44 fields. Considered are four possible models that might explain the steady growth in the number of degrees awarded and the changes that occurred in their distribution by level and by field. Of these, the two most important and distinctive are the "technogenic" model, which interprets the aspiration for degrees as a response to the growth of the economy and its changing demands for various types of highly educated manpower, and the "sociogenic" model, which sees little relationship between changes in the labor market and aspirations for degrees either by level or by field, but rather tends to regard the steady increase in the demand for higher education as a manifestation of constantly increasing desires for upward social mobility. The "sociogenic" model also views the tendency of employers to upgrade their educational requirements, and the upward trend in the proportion of young people aspiring to higher degrees, as twin forces contributing to the phenomenon of "credentialism." Although no decisive conclusion is arrived at, data does not seem to support the technogenic model. (Author/KE)