This document discusses the classification of psychiatric disorders. It defines classification as the process of grouping things based on similarities. In psychiatry, classification aims to enable patient care, communication between professionals, and research, though ideally it would be based on etiology. Major classifications include ICD-10 from WHO and DSM-IV from APA. These take categorical approaches but some argue for dimensional/spectrum models. Classification seeks to group syndromes, disorders, and illnesses while acknowledging limitations due to incomplete understanding of causes.