While Durkheim's The Division of Labor has generated a considerable body of empirical research, the multidimensional concept division of labor lacks both definitional clarity and adequate operational measures. In an attempt to rectify these problems, an open-ended definition approach for specification of the concept and a set of criteria to evaluate the validity of division of labor measures are suggested. The focus is on functional differentiation and current attempts to measure this dimension are evaluated. Theoretical distributions are employed to evaluate the adequacy of division of labor measures. Several shortcomings of the presently employed measures are noted and a statistic based on relative variation is suggested for the functional differentiation dimension of the division of labor.