Reviewing research on the molecular basis of oxygen homeostasis, this text describes the changes in intracellular signalling and gene expression that lead to physiological responses to hypoxia in unicellular, invertebrate, and mammalian species. It examines O2 sensing systems in bacteria and archaea and demonstrates interrelationships among cell proliferation, energy metabolism, oxygen homeostasis, redox states, signal transduction and gene expression in humans and other organisms. The book describes the effect of hypoxia on carotid body structure and function and the effect of alterations in oxygen homeostasis on the pathophysiology of cardiac ischemia, cancer, stroke, and chronic lung disease.