The general principle of interdependence between social factors and demographic behavior is widely recognized at present. Sociologists who have tried to develop a general theory for this relationship do not seem to have entirely succeeded, however. Similarly, attempts to operationalize the intercependence principle have as yet not yielded many results. The author considers that collaboration between the 2 deciplines would be more effective under 2 complementary conditions. On the 1 hand, more attention should be paid to studying the combinations of the levels of the various demographic characteristics (nuptiality, fertility, etc.) that together define the demographic regime of a given population. And, on the other hand, greater attention should be attached to the study of subpopulations, which present greater homogeneity with respect to attitudes and behavior than do national populations and hence better possibilities for identifying a dominant demographic regime. This methodological orientation would facilitate the construction of what American sociologists call theories of the middle range.