Pluripotent stem cells, both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), have the ability to differentiate into several cell types that can be used in drug testing and also in the study and treatment of diseases. These cells can be differentiated by in vitro systems, which may serve as models for human diseases and for cell transplantation. In this review, we address the pluripotent cell types, how to obtain and characterize these cells, and differentiation assays. We also focus on the potential of these cells in clinical trials, and we describe the clinical trials that are underway.