Pharmaceutical excipients are important functional constituents of drug products that accompany the active pharmaceutical ingredient (API) that defines the therapeutic action of a drug product. While the API delivers the therapeutic effect, excipients support this effect by facilitating drug release, increasing drug absorption and increasing patient compliance. This chapter reviews the history and development of excipients with a focus on their development from simple substances used in traditional medicine to their complex application in advanced pharmaceuticals from natural sources. This chapter presents the development of excipients from being considered inert fillers or binders to being vital components that contribute to the functionality of drug products. In addition, this chapter summarises the current legal requirements and the advances made in the development of excipients. There is a special focus on the increasing use of natural (e.g. cellulose, starch), biodegradable (e.g. chitosan, polylactic acid) and green excipients (e.g. alginates, carrageenan) that can meet the present and future needs of the pharmaceutical industry. Examples in this chapter provide evidence of the importance of excipients in the progress of pharmaceuticals. Finally, it looks ahead to the future through considerations of emerging trends like nanotechnology, biocompatible polymers and green chemistry to offer a view of how these functional additives will evolve to influence the future of drug design.