Stem cells have the ability to differentiate into specialized cell subtypes depending upon their level of potency. For instance, embryonic and induced pluripotent stem cells can give rise to cells of all three germ layers: ectoderm, mesoderm, and endoderm. Adult stem cells are generally considered to have limited potency and differentiate into a restricted number of cell types. In order to generate populations of specialized cell types for regenerative medicine, drug screening, or disease and development models, researchers must control and direct the differentiation of stem cells. Cell fate decisions can be directed by natural or chemically synthesized small molecules. For instance, a specific inhibitor of glycogen synthase kinase-3 beta can induce neuronal differentiation in pluripotent stem cells. Combinations of specific cytokines and sodium butyrate, a histone deacetylase inhibitor, have been shown to direct the differentiation of stem cells into hepatocytes. Tocris provides a complete range of bioactive small molecules to control the differentiation of stem cells into defined derivatives.