Energy metabolism is the set of defined biochemical transformations by which living organisms generate energy (in the form of ATP) from nutrients.

The tag energy-metabolism is used for questions specifically concerned with the molecular reactions by which living organisms generate energy from nutrients. This usually implies the generation of ATP, although the production of reduced nucleotide coenzymes is also relevant. The tag energy-metabolism is especially appropriate for questions on substrate-level phosphorylation, the electron transport chain and oxididative phosphorylation, but is also appropriate for other questions, such as those relating to the reactions or processes generating NADH.