Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have promise in regenerative medicine because of their ability to differentiate into all 3 primary germ layers. This review describes recent advances in the understanding of the link between the metabolism of ESCs/iPSCs and their maintenance/differentiation in the cell culture setting, with particular emphasis on amino acid (AA) metabolism. ESCs are endowed with unique metabolic features with regard to energy consumption, metabolite flux through particular pathways, and macromolecular synthesis. Therefore, nutrient availability has a strong influence on stem cell growth, self-renewal, and lineage specification, both in vivo and in vitro. Evidence from several laboratories has documented that self-renewal and differentiation of mouse ESCs are critically dependent on proline metabolism, with downstream metabolites possibly serving as signal molecules. Likewise, catabolism of either threonine (mouse) or methionine (human) is required for growth and differentiation of ESCs because these AAs serve as precursors for donor molecules used in histone methylation and acetylation. Epigenetic mechanisms are recognized as critical steps in differentiation, and AA metabolism in ESCs appears to modulate these epigenetic processes. Recent reports also document that, in vitro, the nutrient composition of the culture medium in which ESCs are differentiated into embryoid bodies can influence lineage specification, leading to enrichment of a specific cell type. Although research designed to direct tissue specification of differentiating embryoid bodies in culture is still in its infancy, early results indicate that manipulation of the nutrient milieu can promote or suppress the formation of specific cell lineages.