Sepsis is among the most common causes of death in patients in intensive care units in North America and Europe. In the United States, it accounts for upwards of 250,000 deaths each year. Investigations into the pathobiology of sepsis have most recently focused on common cellular and subcellular processes. One possibility would be a defect in the production of energy, which translates to an abnormality in the production of adenosine triphosphate and therefore in the function of mitochondria. This article presents a clear role for mitochondrial dysfunction in the pathogenesis and pathophysiology of sepsis. What is less clear is the teleology underlying this response. Prolonged mitochondrial dysfunction and impaired biogenesis clearly are detrimental. However, early inhibition of mitochondrial function may be adaptive.