The history of the regulatory control of pharmaceutical ingredients is briefly reviewed. The impact of legislation, its interpretation through European and international guidelines and resulting licensing policies are discussed. The important role played by excipients in modern formulations is recognised and some examples are given of the unexpected consequences of inappropriate choices. Some data are provided on the extent to which excipients and active ingredients appear in UK-licensed medicines and on the reference standards (pharmacopoeial and non-official) used to control the excipients.