This essay argues that demographic theory over the last half-century has substituted short-term explanations, often focusing on single demographic events, for long-term theory. This means not only that the explanations cannot be employed to forecast the situation in the more distant future, but they are inadequate even for short-term analysis. A basis for a longer-term theory of fertility transition is proposed, employing the concept of social structure and demographic behavior adjusting, slowly and after a considerable lag, to each of three modes of production. The focus is on the transition from agricultural to industrial production, especially as this is occurring in the most advanced industrial societies. Three major conclusions are drawn. (1) Unanticipated fertility changes over the last 50 years can be incorporated within a single demographic transition theory. (2) Societal and demographic changes are still at an early stage of their transition to full adjustment to industrialization. (3) The trend, associated with women's participation in the work force, toward below-replacement fertility will continue, but at some stage most governments will probably attempt to raise fertility to replacement level even if the effort is extremely expensive and slows economic growth.