This guidance describes the Food and Drug Administration’s (FDA’s) Inactive Ingredient Database (IID) and provides recommendations for how to use the IID in the development of drug products. The guidance also describes how the IID can be used in evaluating excipient safety, which can affect application filing and scientific review. In addition, this guidance discusses how the IID is structured; the data regarding excipients in the IID; and how nomenclature, maximum potency levels, and units of measure are presented in the IID. Lastly, the guidance is intended to give IID users a clearer understanding of the database’s benefits and limitations.