Pharmaceutical crops is an ambiguous term used by biologists and chemists for different categories of plants. This review focuses on the definition and scope of pharmaceutical crops. We define pharmaceutical crops as those cultivated species that are used for extraction or preparation of therapeutic substances such as active pharmaceutical ingredients (APIs), excipients used in pharmaceutical formulations, vaccines and antibodies, as well as other therapeutic proteins. Based on the type of pharmaceutical product, these crops can be classified into three distinct yet sometimes overlapping categories: crops for the production of small therapeutic molecules (STMs), large therapeutic molecules (LTMs), or standardized therapeutic extracts (STEs). This review briefly discusses the relationships of pharmaceutical crops with traditional food crops, medicinal plants, medicinal crops, and invasive species. It also addresses the importance, advantages, problems, and challenges of research and development of pharmaceutical crops.