Environmental health has evolved rapidly in recent decades, drawing largely on new analytic technologies, advanced data acquisition and modeling, mechanistic studies in toxicology, and the conceptual framework of risk assessment. The latter combines toxicologic and epidemiologic data with improved techniques for quantifying exposure, producing estimates of risks from environmental hazards or conditions to selected target populations. The public and governments have become increasingly concerned with environmental health and quality. The major lessons have been (a) environmental-health scientists must participate in policy debates; (b) environmental health problems are exceedingly complex and require interdisciplinary research; and (c) environmental health is a global issue. The globalization of commerce, the untested impact of international trade agreements, increased migration, and especially increased population, have profound impact on the quality as well as availability of air, water, land, and food. Global atmospheric transport of pollutants and the effect on atmosphere and climate are two examples of globalization of environmental health.