The sciences are divided into two main groups—the natural sciences, which deal with nature, or the physical world; and the social sciences, which study human society and behavior, or the social world. The natural sciences, in turn, can be subdivided into the physical sciences, studies concerned with nonliving matter; and the biological, or life, sciences, studies dealing with living matter. Each of these subdivisions is in turn divided into various branches with a number of specialized areas of study.

The physical sciences include such areas of study as physics, chemistry, engineering, astronomy, geology, oceanography, and meteorology. A grouping within the physical sciences, the earth sciences, is made up of geology, oceanography, meteorology, and those parts of astronomy, engineering, and other fields that deal with the earth as a physical object. (Mathematics was formerly regarded as a physical science but is now usually regarded as a tool of science, rather than a science.)

The biological sciences include such fields as botany, zoology, physiology, medicine, forestry, genetics, agronomy, and animal husbandry.

Included within the social sciences are sociology, economics, education, and political science. History is sometimes classed as a social science, sometimes as one of the humanities.

Anthropology, geography, and psychology deal with both physical and social facts. Physical anthropology, physical geography, and physiological psychology are usually called natural sciences. Cultural anthropology, human geography, and the nonphysiological fields of psychology are classed as social sciences.

Another grouping, the behavioral sciences, is made up of major portions of sociology, anthropology, and psychology, and the areas of political science, economics, geography, biology, law, and other fields specifically concerned with human behavior.

When scientists attempt to solve specific problems in order to discover facts of practical use, they are practicing applied science. Examples of applied sciences are engineering, medicine, forestry, and animal husbandry.

Studies that are undertaken to discover facts without regard to their immediate usefulness or value are called pure, or basic, science. Examples of pure sciences are physics, physiology, botany, and zoology. Much of pure science is motivated by scientific curiosity alone. However useless or unrelated to immediate problems pure scientific research may seem to be, scientists recognize that all scientific development is ultimately based on such far-reaching and imaginative studies.