Human organoids hold tremendous potential for biomedical applications1,2,3 (Fig. 1a,b). These three-dimensional structures of cultured cells recapitulate important aspects of in vivo organ development and biological function. They provide tractable in vitro models of human physiology and pathology, thereby enabling interventional studies that are difficult or impossible to conduct in human subjects. For example, organoids allow genetic and pharmacological manipulation in a complex cellular context that reflects human biology, and they enable investigations of the early stages of organ development and disease onset. Human organoids complement (and may eventually replace) animal models in many areas of preclinical drug development. Moreover, they provide patient-specific ‘avatars’ for drug development and precision therapies, including treatments for cancer, rare genetic diseases (such as cystic fibrosis) and complex multifactorial disorders (such as epilepsy). Finally, they promise to contribute to regenerative medicine, with the goal of producing functional biological structures that can be transplanted into patients.