Improving global health is beneficial to both rich and poor countries. It is vital to economic development, global security against emerging infections, and political stability in countries ravaged by famine and disease. A new generation of economists tells us that investments in disease prevention and healthcare in the developing world can bring substantial returns in economic growth and poverty reduction to these countries. Health systems in developing countries are facing major challenges in the 1990s and beyond because of a growing epidemiological diversity as a consequence of rapid economic development and declining fertility. The infectious and parasitic diseases of childhood must remain a priority at the same time the chronic diseases among adults are emerging as a serious problem. New epidemic diseases like AIDS are emerging, and the health of the poor during the economic crisis is a growing concern. These health developments intensify the need for better information on the effectiveness and cost of health interventions. Chronic diseases already pose a substantial economic burden, and this burden will evolve into a staggering one over the next two decades, although high-income countries currently bear the biggest economic burden of chronic diseases, countries in the developing world, especially middle-income, are expected to assume an increasing share as their economies and populations grow and the marginal costs for governments of achieving maximal adult survival are rising, in contrast to declines in marginal costs of achieving child survival.