The authors define the industrial system as a central object of economic activity of contemporary socio-economic systems, whose operation is directly linked to the functioning of big integrated structures. The article emphasizes the significance of the problem of increasing energy efficiency of industrial systems in the contemporary Russian economy. The authors analyze modern approaches to energy efficiency assessment used in the world science; in particular, they study approaches adopted by the International Energy Agency, the World Energy Council, Asian-Pacific Research Centre, the French Environment and Energy Agency and a number of others, look at their advantages and disadvantages. The authors present their own approach to energy efficiency assessment of industrial systems based on three-level assessment: the level of the industrial system as a whole, the level of specific kinds of goods produced by the industrial system and the level of technological processes of goods manufacturing. The article outlines the authors’ system of energy efficiency indicators for industrial systems grouped in accordance with the different levels of assessment and factors of “green economy”. The article suggests procedures and approaches to conducting the composite (integral) assessment of energy efficiency at different levels, with their interaction and mutual influence taken into account. The authors tested the proposed methodological approach by assessing the energy efficiency of Russia’s biggest industrial system, the Ural Mining and Metallurgical Company (UMMC) engaged in the production of copper and copper products. The studies provided grounds for conclusions and suggestions as to the direction of further studies.