The concepts of personality and personality disorder have been defined and classified in many different ways from different perspectives from past to present. Over time, international classification systems such as DSM and ICD have been developed and a common framework for the classification of personality disorders has been tried to be established. Personality disorders can significantly affect an individual's functionality, relationships and quality of life. Therefore, studies on better understanding of personality disorders and diagnostic processes are gaining importance. In this context, the main purpose of this article is to make a review on personality disorders. In this article, definitions of personality, personality theories, personality traits and personality disorders are examined and diagnostic changes in the current versions of classification systems are discussed through ICD-11, DSM-5 and alternative DSM-5 Model for Personality Disorders. The main features and diagnostic criteria of these personality disorders are examined in detail. In addition, existing theories and studies on personality disorders are also discussed. Finally, the characteristics of the measurement tools used in the assessment of personality disorders are emphasized. This article aims to contribute to the body of knowledge in the field of personality disorders by providing both a theoretical and practical perspective. As a result of the study, it was observed that the dimensional approach was emphasized in international diagnostic systems related to personality disorders instead of the commonly used categorical approach. In parallel with this, it is also among the results of the study that various measurement tools have been developed to be used in the diagnosis of personality disorders according to the dimensional approach.