International Classification of Diseases (ICD)

This article presents the history, contents, structures, functions, and applications of the International Classification of Diseases (ICD), which is a global standard maintained by the World Health Organization (WHO). The article aims to present ICD from the knowledge organization perspective and focuses on the current versions, ICD-10 and ICD-11. It also introduces the relationship between ICD and other health knowledge organization systems (KOSs), plus efforts in research and development reported in health informat-ics. The article concludes that the high-level effort of promoting a unified classification system such as ICD is critical in providing a common language for systematic recording, reporting, analysis, interpretation, and comparison of mortality and morbidity data. It greatly enhances the constancy of coding across languages, cultures, and healthcare systems around the world.