The contents of this volume summarize the large body of data produced by a project dealing with socio-economic inequalities in health, nutrition, and population (hnp) within fifty-six developing countries. The data are intended to serve as a source of basic information for use in preparing analyses and developing initiatives to benefit poor people. At the volume's core are the overview tables in the following section. Each overview table provides figures dealing with inequalities across economically-defined quintiles of the population for a single hnp indicator for all of the fifty-six countries covered. The 120 indicators presented are in four categories: health status (such as infant and child mortality, child nutritional level, and fertility); use of basic health services (immunization, treatment of common childhood illnesses, antenatal care, and assisted delivery); health-related behaviors (e.g., smoking and alcohol use and sexual practices); and other health-status determinants (like education). The purpose of this opening chapter is to explain how data appearing in the overview tables and in the individual country reports came into being, and how they can be used to help shape policies and programs. To this end, it deals with four topics. The first is the rationale for the tables' focus on the economic dimension of health inequalities. The second is the source of the data and the methods used to produce the tables. Third shows illustrations of how the information presented in the tables can be used to facilitate health policy and program development. The fourth shows how the techniques used in producing the information can be used to monitor how well or poor programs or policies have reached the poor.