This chapter focuses on the metabolic framework that sustains pluripotent stem cells in culture, potential mechanisms that regulate the physiology of these cells, and the effect of environmental factors on homeostasis in these cells. Induced pluripotent stem (iPS) cells promise enormous potential for the generation of cells for regenerative medicine, drug discovery, and understanding disease etiology. Cellular responses to changes in oxygen involve the regulation of hypoxia-inducible factors (HIFs). HIFs are activated in cells in low oxygen concentrations. HIF activation has been shown to increase exponentially once oxygen concentrations drop below 7% oxygen, with maximal activation at 0.5%. HIFs reprogram metabolism to ensure continued energy production at low oxygen concentrations via the regulation of transcription, including the upregulation of genes involved in glycolytic metabolism. The unique metabolism of pluripotent stem cells predicates that they may not respond to medium formulations and supplements like somatic cells.