The branch of psychology that specializes in the research, assessment, diagnosis, evaluation, prevention, and treatment of emotional and behavioral disorders. These psychologists are doctorate-level professionals who have received training in research methods and techniques for the diagnosis and treatment of various psychological disorders. They work primarily in health and mental health clinics, in research, in academic settings, or in group and independent practices. They also serve as consultants to other professionals in the medical, legal, social-work, and community-relations fields. These psychologists comprise approximately one third of the psychologists working in the United States and are governed by the code of practice of the American Psychological Association and by state licensing requirements.

This domain includes any theory of mind that focuses on mental activities, such as perceiving, attending, thinking, remembering, evaluating, planning, language, and creativity, or any theory that suggests a model for the various processes involved.

The branch of psychology that specializes in facilitating personal and interpersonal functioning across the lifespan. This psychology focuses on emotional, social, vocational, educational, health-related, developmental, and organizational concerns—such as improving well-being, alleviating distress and maladjustment, and resolving crises—and addresses issues from individual, family, group, systems, and organizational perspectives. This psychologist has received professional education and training in one or more areas, such as educational, vocational, employee, aging, personal, marriage, or rehabilitation counseling. In contrast to a clinical psychologist (see clinical psychology), who usually emphasizes origins of maladaptations, this psychologist emphasizes adaptation, adjustment, and more efficient use of the individual’s available resources.

The branch of psychology that studies the changes—physical, mental, and behavioral—that occur from conception to old age and investigates the various biological, neurobiological, genetic, psychological, social, cultural, and environmental factors that affect development throughout the lifespan. Since its emergence as a formal discipline in the late 19th century, the field has broadened its focus from one that largely emphasized infant, child, and adolescent development to one that also accounted for adult development and the aging process and, more recently, prenatal development.

A branch of psychology dealing with the application of psychological principles and theories to a broad spectrum of teaching, training, and learning issues in school settings. This psychology also addresses psychological problems that can arise in these systems. These psychologists often hold applied as well as academic positions, spending their time in a variety of teaching, research, and applied pursuits.

The scientific study of behavior, motives, or cognition in a laboratory or other controlled setting in order to predict, explain, or influence behavior or other psychological phenomena. This psychology aims at establishing quantified relationships and explanatory theory through the analysis of responses under various controlled conditions and the synthesis of adequate theoretical accounts from the results of these observations.

The branch of psychology that studies human behavior in the work environment and applies general psychological principles to work-related issues and problems, notably in such areas as personnel selection, personnel training, employee evaluation, working conditions, accident prevention, job analysis, job satisfaction, leadership, team effectiveness, and work motivation.

The branch of psychology that systematically investigates the nature and definition of as well as its development, its structure and trait constructs, its dynamic processes, its variations (with emphasis on enduring and stable individual differences), and its maladaptive forms (i.e., disorders). The field rests on a long history of theoretical formulation (e.g., trait theories, psychoanalytic theories, role theories, learning theories, type theories) that has aimed to synthesize cognitive, emotional, motivational, developmental, and social elements of human individuality into integrative frameworks for making sense of the individual human life. It has also developed numerous tests and assessments to measure and understand aspects of .

The branch of psychology concerned with the quantification and measurement of mental attributes, behavior, performance, and the like, as well as with the design, analysis, and improvement of the tests, questionnaires, and other instruments used in such measurement.

The study of how an individual’s thoughts, feelings, and actions are affected by the actual, imagined, or symbolically represented presence of other people. Psychological differs from sociological in that the former tends to put greater emphasis on internal psychological processes, whereas the latter focuses on factors that affect social life, such as status, role, and class.

A field of psychological theory and research that focuses on the psychological states (e.g., contentment, joy), individual traits or character strengths (e.g., intimacy, integrity, altruism, wisdom), and social institutions that enhance subjective well-being and make life most worth living. A manual, Character Strengths and Virtues: A Handbook and Classification, serves this perspective in a manner parallel to the Diagnostic and Statistical Manual of Mental Disorders for the categorization of mental illness.