Child development is the study of all aspects of human growth and change. It is an interdisciplinary, scientific, and applied field of study. Researchers often divide the subject of development into three broad domains--physical, cognitive, and emotional and social--through five periods of development from conception through adolescence.

Theories provide organizing frameworks that guide and give meaning to the scientific study of children. Major theories can be organized according to the stand that they take on four basic issues: (1) Is the course of development continuous or discontinuous? (2) Is there one general course of development that characterizes all children, or are there many possible courses? (3) Are genetic or environmental factors more important in determining development? (4) Do individual children establish stable, lifelong patterns of behavior early in development, or are they open to change? Many theories, especially modern ones, take a balanced point of view and recognize the merits of both sides of these issues.

In recent years, the field of child development has become increasingly concerned with applying its knowledge to the solution of pressing social problems faced by children and adolescents. Public policy, laws, and government programs designed to improve current conditions are essential for protecting children's development.