Personality disorders are patterns of perceiving, relating to, and thinking about the environment and oneself that are negative, abnormal, or stressful. They typically persist over time and involve perceptions, thoughts, and behaviors upsetting to the individual who experiences them and which cause significant problems in the person's relationships and professional and social activities. They can include antisocial behavior, acute shyness or sensitivity, negative perceptions, and more severe forms, such as paranoia or schizophrenia. Personality Disorders, Second Edition defines and explains these behavioral patterns, which are organized into three types, or clusters, the social and medical issues related to them, and how doctors can treat them.