Psychologists study human behavior in their undergraduate and postgraduate degrees however, many have postgraduate qualifications or doctoral level qualifications in clinical psychology. Clinical psychologists have specialist training in psychological assessment and therapy with diagnosed psychiatric and/or mental disorders.

Psychologists generally assist people with a range of everyday problems such as stress and relationship difficulties. They also provide counseling and therapy for people with diagnosed mental disorders, such as anxiety disorders or depression. They help people to develop the skills needed to cope and function better, and to prevent ongoing problems.

Clinical psychologists and psychologists cannot prescribe medication. Their treatments are based on changing behavior and emotional responses without medication. There is a considerable amount of evidence showing psychological treatments are effective on their own, as well as in combination with certain types of medication.

Psychiatrists have a medical degree, which involved six years of studying general medicine, followed by further study to specialize in the diagnosis and treatment of mental illness and emotional problems. Psychiatrists treat the effects of emotional disturbances on the body and the effects of physical conditions on the mind. Psychiatrists can prescribe medication. Some combine medication with other forms of therapy.

Psychotherapy is the use of psychological methods, particularly when based on regular personal interaction, to help a person change and overcome problems in desired ways. Psychotherapy aims to improve an individual's well-being and mental health, to resolve or mitigate troublesome behaviors, beliefs, compulsions, thoughts, or emotions, and to improve relationships and social skills. Certain psychotherapies are considered evidence-based for treating some diagnosed mental disorders.

There are over a thousand different psychotherapy techniques, some being minor variations, while others are based on very different conceptions of psychology, ethics (how to live) or techniques. Most involve one-to-one sessions, between client and therapist

Psychometrics is a field of study concerned with the theory and technique of psychological measurements.

The field is concerned with the objective measurement of skills and knowledge, abilities, attitudes, personality traits, and educational achievement. Some psychometric researchers focus on the construction and validation of assessment instruments such as questionnaires, tests, raters' judgments, and personality tests. Others focus on research relating to measurement theory (e.g., item response theory; intraclass correlation).