The central series of chemical reactions in cellular energy metabolism, also known as the citric acid cycle or tricarboxylic acid cycle. Taking place in the mitochondria, it oxidises the breakdown products of carbohydrates, fats, and amino acids, releasing carbon dioxide and generating energy-carrying molecules that drive the production of ATP, the cell’s energy currency. Named after Hans Krebs, who elucidated it in 1937, the cycle is the final common pathway for the complete oxidation of food fuels. Its intermediates also serve as building blocks for synthesising amino acids and other molecules, making it a hub of both energy production and biosynthesis.