This report describes the historic development of the disease nomenclatures and classifications that ultimately became the major international standard known as the World Health Organization's (WHO) International Classification of Diseases (ICD). Written largely at the initiative of Dr. Iwao Moriyama, a participant in these developments for much of the 20th century, the report describes the historical, cultural, and scientific environment in which ICD evolved, expanded, and improved. Although the report focuses on the application of ICD to mortality, it also touches on nonmortality applications, particularly as these affected the classification for mortality.