As knowledge of modern medicine and human health evolves, so too must the clinical terminology that supports it. As health data is collected about individuals over many years, and even decades, it is imperative that the meaning of codes recorded in the past remain unchanged indefinitely into the future. This ensures that health data can be effectively retrieved and analysed irrespective of when it was recorded. This is important not only for the provision of healthcare, the management of population health, and conducting clinical research, but also for medicolegal purposes. This chapter explains the mechanisms by which SNOMED CT® supports these important history and versioning requirements.