Personality disorders are a group of psychiatric conditions involving enduring and substantial deviations in a person's thinking patterns, emotional experience, way of relating to others, and behaviour. They usually begin in adolescence or early adulthood and are defined as long-term conditions.

Personality disorders are classified according to criteria set out in diagnostic manuals such as the DSM-5 and ICD-10. These guides divide personality disorders into three main clusters: A, B, and C. Disorders in each cluster have distinct features. Some examples include:

Cluster A (Paranoid, Schizoid, Schizotypal):

Paranoid Personality Disorder: Involves excessive suspiciousness, distrust, and hostility.
Schizoid Personality Disorder: Characterised by social isolation and emotional detachment.
Schizotypal Personality Disorder: Tendency toward odd, eccentric, or mildly paranoid thinking.

Cluster B (Antisocial, Borderline, Histrionic, Narcissistic):

Antisocial Personality Disorder: Tendency to disregard the rights of others, violate legal norms, lie, and engage in criminal behaviour.
Borderline Personality Disorder: Involves instability in relationships, intense emotional variability, identity disturbance, and self-harming behaviour.
Histrionic Personality Disorder: Tendency to exaggerate emotional expression, seek attention, and behave dramatically in relationships.
Narcissistic Personality Disorder: Features include grandiosity, exploitation of others, lack of empathy, and disregard for others' rights.

Cluster C (Dependent, Obsessive-Compulsive):

Dependent Personality Disorder: Involves excessive reliance on others, difficulty making decisions, and constant need for approval.
Obsessive-Compulsive Personality Disorder: Tendency toward perfectionism, orderliness, need for control, inflexibility, and excessive focus on detail.

Each personality disorder is characterised by specific symptoms and behaviours. However, diagnosis should be made by a psychiatrist or clinical psychologist, as these disorders can resemble one another and may be complex. Treatment usually involves a personalised approach combining therapy and sometimes medication.