Abstract: We examine the reduced-form relationship between per capita income and various environmental indicators. Our study covers four types of indicators: urban air pollution, the state of the oxygen regime in river basins, fecal contamination of ri'ver basins, and contamination of river basins by heavy metals. We find no evidence that environmental quality deteriorates steadily with economic growth. Rather, for most indicators, economic growth brings an initial phase of deterioration followed by a subsequent phase of improvement. The turning points for the different pollutants vary, but in most cases they come before a country reaches a per capita income of $8000. I. INTRODUCTION Will continued economic growth bring ever greater harm to the earth's environment? Or do increases in income and wealth sow the seeds for the amelioration of ecological problems? The answers to these questions are critical for the design of appropriate development strategies for lesser developed countries. Exhaustible and renewable natural resources serve as inputs into the production of many goods and services. If the composition of output and the methods of production were immutable, then damage to the environment would be inextricably linked to the scale of global economic activity. But substantial evidence suggests that development gives rise to a structural transformation in what an economy produces (see Syrquin [1989]). And societies have shown remarkable ingenuity in harnessing new technologies to conserve scarce resources. In principle, the forces leading to change in the composition and techniques of production may be sufficiently strong to more than offset the adverse effects of increased economic activity on the environment. In this paper we address this empirical issue using panel data on ambient pollution levels in many countries. Examination of the empirical relationship between national income and measures of environmental quality began with our *We thank the Ford Foundation, the Sloan Foundation, the John S. Guggenheim Memorial Foundation, the Institute for Policy Reform, and the Centers of International Studies and of Economic Policy Studies at Princeton University for financial support. We are grateful to Peter Jaffee, who tutored us on the various dimensions of water quality, to Robert Bisson, who provided us with the GEMS/ Water data, and to seminar participants at the O.E.C.D. Development Centre and the Institute for International Economic Studies in Stockholm, Sweden, who gave us helpful comments and suggestions. Special thanks go to James Laity, whose research assistance was simply extraordinary.