Each branch of psychology has many explanations for psychopathology, including failure of self-realization (humanistic), unconscious conflict (psychodynamic), cognitive biases (cognitive), and biochemical imbalances (psychobiological). Although some people may believe that fate plays a role in whether someone develops a disorder, fate is not a scientific phenomenon that any branch of psychology includes in the study of psychopathology.

The medical or biomedical theory of abnormality views the causes of abnormal psychology to be biological as well as the symptoms and cures. Examples of this might include hormone imbalances or differences in brain structure. Unconscious conflict would be classified under the psychanalytic psychology, attachment theory under social or developmental psychology, conditioning under behavioral psychology, and thought patterns under cognitive psychology. 

There are higher rates of mood and anxiety disorders in women for a combination of reasons, including hormonal differences, higher rates of sexual assault, less societal power and control, and more willingness to get help (which increases the rates, though not the occurances). The average woman is less aggressive than the average man, but that does not relate to anxiety/mood disorders and in fact brings down the rates of other types of disorders, such as antisocial personality disorder.

The major paradigm for dissociative disorders is the diathesis-stress model. This model depends on the idea that psychological disorders occur when a person is predisposed to the disorder and experiences significant stress. Research has indicted that many dissociative patients experienced childhood physical or sexual abuse, which were the cause of significant stress. According to this model, these patients also had a predisposition, or diathesis, to dissociate easily. This means they are easily hypnotized and prone to engage in fantasy. Dissociation was a method of avoidance for these patients. In other words, dissociating from reality allowed them to escape their stressful experiences, protect themselves from emotional trauma, and block out unpleasant memories. 

Biological theorists believe that generalized anxiety disorder is caused chiefly by biological factors. One associated belief is that, due to low activity of the neurotransmitter gamma-aminobutyric acid (GABA), excessive worrying and anxiety manifests in a person. Biological treatments for generalized anxiety disorder include antianxiety drug therapy, relaxation training, and biofeedback.

A double blind study is a study in which information that may change the results is kept both from the experimenter and from the participant. This is to keep the results of the study as neutral and unbiased as possible. 

Axis IV records "psychological stressors" or external events that happen in a person's life that causes them to have a psychological problem. Debt, such as the inability to pay hostpital bills, would fall on this axis.

Axis I refers to the principle disorder that needs attention, such as major depressive disorder. Axis II lists any personality disorders that may be causing the problem described in Axis I. An example of a disorder that would be listed under Axis II is paranoid personality disorder. Axis III lists any medical or neurological problems that would be relevant to the patient's psychological problems. An example of a problem that would be listed under Axis III is severe asthma.

Comorbidity occurs when a patient has multiple diagnoses. Comorbidity is common in psychology, in that most patients have multiple diagnoses (e.g., ADHD & ODD) because psychiatric illnesses typically occur together. 

A uniform system for classifying and describing mental disorders has been developed by the American Psychiatric Association. It is called the Diagnostic and Statistical Manual of Mental Disorders.

The American Medical Association maintains the Current Procedural Terminology (CPT) code set, which is a set of codes that describes medical, surgical, and diagnostic services. The International Classification of Disease (ICD) is used to classify diseases and other health problems. Medicare mandates the use of the Healthcare Common Procedure Coding System (HCPCS) for reimbursement. The United States Pharmacopeia (USP) is a compendium of over-the-counter and prescription drugs. 

Insanity is the legal term for a severe mental illness, present at the time a crime was committed, that impaired the defendant's capacity to understand the moral wrong of an act. Insanity is not a medical diagnosis.

Idiocy is any severe mental deficiency present in early childhood. Dementia is a progressive loss of mental function characterized by memory impairment. A psychosis is a mental disorder in which there is a severe loss of contact with reality; it is a common feature of schizophrenia. A neurosis is an unconscious conflict that produces anxiety and leads to the use of defense mechanisms.