Psychology is a broad discipline, essentially spanning subject matter from biology to sociology. Psychologists study the intersection of two critical relationships: one between brain function and behavior, and one between the environment and behavior.

Psychology is a tremendously varied field. Psychologists conduct both basic and applied research, serve as consultants to communities and organizations, diagnose and treat people, and teach future psychologists and other types of students. They test intelligence and personality. Many psychologists work as health care providers. They assess behavioral and mental function and well-being, stepping in to help where appropriate. They study how human beings relate to each other and also to machines, and they work to improve these relationships. Finally, with the U.S. undergoing large changes in its population makeup, psychologists bring important knowledge and skills to understanding diverse cultures.

Psychologists traditionally study both normal and abnormal functioning, and also treat patients with mental and emotional problems. They also concentrate on behaviors that affect the mental and emotional health and mental functioning of healthy human beings. Many psychologists work independently. They also team up with other professionals -- for example, other scientists, physicians, lawyers, school personnel, computer experts, engineers, policymakers, and managers--to contribute to every area of society. Thus we find them in laboratories, hospitals, courtrooms, schools and universities, community health centers, prisons, and corporate offices.

Opportunities for work in psychology are expanding in number and scope, especially for those with graduate degrees, while an undergraduate degree remains excellent preparation for continued graduate work in psychology or for another field, such as business, medicine, or computer science. The move toward preventing illness, rather than merely diagnosing and treating it, requires people to learn how to make healthy behavior a routine part of living. Indeed, many of the problems facing society today are problems of behavior, for example, drug addiction, poor personal relationships, violence at home and in the street, and the harm we do to our environment. Psychologists contribute solutions to problems through careful collection of data, analysis of data, and development of intervention strategie--in other words, by applying scientific principles, the hallmark of psychology.

A doctoral degree usually is required for employment as an independent licensed clinical or counseling psychologist. Psychologists with a Ph.D. qualify for a wide range of teaching, research, clinical, and counseling positions in universities, health care services, elementary and secondary schools, private industry, and government. Psychologists with a Doctor of Psychology (Psy.D.) degree usually work in clinical positions or in private practices, but they also sometime teach, conduct research, or carry out administrative responsibilities.

A specialist degree is required in most States for an individual to work as a school psychologist, although a few States still credential school psychologists with master's degrees. A specialist (Ed.S.) degree in school psychology requires a minimum of 3 years of full-time graduate study (at least 60 graduate semester hours) and a 1-year internship. Because their professional practice addresses educational and mental health components of students' development, school psychologists' training includes coursework in both education and psychology.

Persons with a master's degree in psychology may work as industrial-organizational psychologists. They also may work as psychological assistants under the supervision of doctoral-level psychologists and may conduct research or psychological evaluations. A master's degree in psychology requires at least 2 years of full-time graduate study. Requirements usually include practical experience in an applied setting and a master's thesis based on an original research project.

A bachelor's degree in psychology qualifies a person to assist psychologists and other professionals in community mental health centers, vocational rehabilitation offices, and correctional programs. Bachelor's degree holders may work as research or administrative assistants for psychologists. Some work as technicians in related fields, such as marketing research. Many find employment in other areas, such as sales or business management.

The U.S. Bureau of Labor Statistics expects that opportunities in psychology will continue to grow over the next decade. Employment in health care will grow fastest in outpatient mental health and substance abuse treatment clinics. Numerous job opportunities will also arise in schools, public and private social service agencies, and management consulting services. Companies will use psychologists' expertise in survey design, analysis, and research to provide marketing evaluation and statistical analysis. The increase in employee assistance programs, which offer employees help with personal problems, also should spur job growth.

Growing awareness of how students mental health and behavioral problems, such as bullying, affect learning is increasing demand for school psychologists to offer student counseling and mental health services. Clinical and counseling psychologists will be needed to help people deal with depression and other mental disorders, marriage and family problems, job stress, and addiction. The rise in health care costs associated with unhealthy lifestyles, such as smoking, alcoholism, and obesity, has made prevention and treatment more critical. An increase in the number of employee assistance programs, which help workers deal with personal problems, also should spur job growth in clinical and counseling specialties. Industrial-organizational psychologists will be in demand to help to boost worker productivity and retention rates in a wide range of businesses. Industrial-organizational psychologists will help companies deal with issues such as workplace diversity and antidiscrimination policies. Companies also will use psychologists' expertise in survey design, analysis, and research to develop tools for marketing evaluation and statistical analysis.

According to the BLS, median annual earnings of wage and salary clinical, counseling, and school psychologists in May 2004 were $54,950. The middle 50 percent earned between $41,850 and $71,880. The lowest 10 percent earned less than $32,280, and the highest 10 percent earned more than $92,250.