Public health is the art and science of preventing disease, prolonging life, and promoting health through the organized efforts of society. The goal of public health is the biological, physical, and mental well-being of all members of society. Thus, public health must address the challenge of confronting health problems, as well as political, social, and economic factors affecting health, not only at the community, state, and national levels, but also at the global level. This chapter introduces the reader to the scope and current major concerns of public health in the twenty-first century, giving examples of each. It is the goal of this chapter to assist the reader in understanding the conceptual framework of the field, which will help them in placing the subsequent more detailed chapters into the context of the entire field of public health.