This paper explores several related propositions about rural economic life and demographic change. A central thesis is that the shrinking of the farm labor force associated with past processes of economic development led to lower fertility. A subsidiary thesis is that this effect may no longer be essential to cause fertility decline; government population policies can substitute for it. This paper emphasizes two features of the transition in now-industrial countries: (1) the rising costs and falling benefits to parents of having many children, and (2) the link of that change to productivity growth in and structural change away from farming. Labor-saving innovations on farms lessened the benefits of children, causing the main fertility transition. Women left unpaid family labor on farms to work in offices, factories, and shops; this shift depressed fertility as jobs interfered with child care. Jobs for children were fewer in urban than rural settings, so more children attended school, and most parents decided to have fewer but better-educated children. The annex describes world and regional estimates of gross and per capita product for selected dates from 1800 to 1980 and projections the the year 2000.