Pediatric drug development has evolved since the original guidance E11 Clinical Investigation of Medicinal Products in the Pediatric Population (ICH E11 (2000)) published, requiring consideration of regulatory and scientific advances relevant to pediatric populations. This addendum does not alter the scope of the original guidance. ICH E11 (2000), including this addendum (R1); is not intended to be comprehensive; other ICH guidances, as well as documents from regulatory authorities worldwide, the World Health Organization (WHO), and pediatric societies, provide additional detail. The purpose of the addendum is to complement and provide clarification and current regulatory perspective on topics in pediatric drug development.