In this section, we discuss two types of pluripotent mammalian cells: embryonic stem (ES) cells and induced pluripotent stem (iPS) cells. Our focus is on the network of genes and proteins that regulate the pluripotent state of these cells and can subsequently lead to multiple types of differentiated cells. In culture, these two types of pluripotent cells can be used to form specific types of differentiated cells for research purposes or, potentially, as “replacement parts” for worn-out or diseased cells in patients. iPS cells can be formed from patients with many types of diseases and then differentiated into the specific cell type affected by the disease; here we see how study of such cells can illuminate crucial underlying causes of a specific individual’s disease.