A brief outline is given of how various types of adaptation of the ICD for use in different situations have arisen. The application includes condensed lists, national adaptations, studies of morbidity, specialty adaptations (including for primary care), and augmentation by supplementary material. The major purposes of different applications are reviewed and an indication is given of factors influencing selection of the condition of primary interest in such situations. The article concludes by suggesting guidance for the development of applications and adaptations of the ICD.