Based upon the currently emerging international consensus on how to account for the materials flows of industrialized countries, this article proposes methods to account for the energetic metabolism of societies. It argues that, to fully exploit the potential of the metabolism approach in the context of sustainable development, both energetic and material aspects of societal metabolism have to be taken into account. The article proposes concepts to empirically describe energy input, internal energy transformations, and energy utilization of societies by extending commonly used notions of energy statistics in a way that is compatible with current methods of materials flow analysis. Whereas energy statistics include only the energy used in technical devices for providing heat, light, mechanical work, and data processing, an accounting system for the energetic metabolism of societies should also consider flows of nutritional energy for both livestock and humans. Moreover, in assessing the energy input of a society, all inputs of energy‐rich materials (and immaterial forms of energy such as electricity and light) that cross the boundary into the biophysical structures of society should be taken into consideration, regardless of the purpose for which they are eventually used. As a consequence, an energetic metabolism accounting system treats all biomass as energy input, instead of considering only the biomass used for technical energy generation, as energy statistics do. Part II in this set of articles will apply these concepts to different modes of societal organization and explore the significance of energetic metabolism for sustainable development. In particular, it will explore the significance for policies that aim at increasing the contribution of renewable energy, especially biomass.