Thailand from 1960 to 2005 achieved fast economic growth and a rapid decline of income poverty. It also did well at raising educational attainment, improving family planning, expanding access to safe water and adequate sanitation, and delivering basic health services and nutritional assistance to the poor. Not surprisingly, then, Thailand from 1960 to 2005 had one of the steepest infant mortality declines in the world. Thailand's success at reducing infant mortality, this study finds, was due as much to the effective public provision of basic social services as to rapid economic growth or poverty decline. Political liberalization and democratization contributed in a variety of ways to the effective public provision of basic social services, not just through electoral incentives, but also by providing an environment in which pro-poor issue networks could coalesce and advocate improvements in social policies, and by contributing to the political mobilization of impoverished people, which helped to improve social policies from the demand side. Note: This paper is adapted from a chapter of a book manuscript that explores the impact of economic factors (GDP per capita growth, income inequality, and income poverty) and the provision of basic social services (particularly basic health care, but also nutritional intervention, education, family planning, safe water, and sanitation) on the pattern and pace of mortality decline from 1960 to 2005 in eight middle-income developing societies, four in Latin America (Argentina, Brazil, Chile, and Costa Rica) and four in East Asia (Taiwan, South Korea, Indonesia, and Thailand)