Beginning in 1940, Mexico enjoyed a 30-year period of sustained economic growth; on the demographic side, this interval was characterized by sustained high fertility and rapidly falling mortality. By the early 1980s, the country faced crises of liquidity and inflation; a fertility decline had set in after the early 1970s. This assessment of four decades of economic, social, and demographic change explores reasons why fertility remained high in the face of rapid development; how demographic change contributed to the current economic crisis; and why fertility declined precipitously in the most recent period. The authors argue that development policy helped perpetuate high fertility for several decades; population policy, they believe, exerted an identifiable downward influence on Mexican fertility.