The validation of a commercial process to manufacture active pharmaceutical ingredients (APIs) and their intermediates starts during the development process. A number of systems supporting the preparation of APIs for clinical trials must be validated. The data supporting the eventual process validation must be robust and could be inspected by regulatory authorities. For these reasons it is imperative that chemists involved in these activities have a good understanding of the requirements for validation at the development level, what is required to validate a chemical process and the support that is required at the manufacturing site.