This paper provides an overview of the leading role that energy efficiency plays in the development of modern socioeconomic systems, which serve as the foundation for building green economies. The main purpose of the paper is to develop a methodological toolkit for assessing energy efficiency of large industrial complexes and test it on the world's largest metallurgical complexes. The central object of the research is the Ural Mining and Metallurgical Company (UMMC), which mainly specializes in the production of copper and copper-based products. The study follows a comparative analysis of a set of preliminary selected energy efficiency indicators obtained from UMMC with those of the world's leading copper manufacturers and copper-based products. At the same time, in accordance with the methodical approach, it is proposed to divide the energy efficiency indicators of an industrial complex into three levels: the level of an industrial complex as a whole (1); the level of certain types of products manufactured in the industrial complex (2); the level of the technological process (3). To obtain summarized (synthetic) energy efficiency estimates of the industrial complex, the hierarchy analysis method has been proposed. For the comparative analysis of energy efficiency indicators of UMMC, the authors chose the following companies: Norilsk Nickel and Russian Copper Company and leading world companies, such as Glencore Xstrata Plc (Switzerland), Codelco (Chile), KGHM Polska Miedz SA (Poland), and Vedanta Resources (India). The obtained results revealed that UMMC strongly lags behind in a number of key energy efficiency indicators. During 2010-2016, a negative trend was observed in the majority of UMMC enterprises. The results also showed the practical applicability of the given methodical approach and the possibility of its wide use in solving energy efficiency problems of Russian industrial complexes for their strategic development. Keywords: copper producers, energy efficiency, energy efficiency indicators, green and low-carbon economy, industrial complex. 'The Future We Want' [4], the main features of a green economy model are resource efficiency, low carbon emissions, preservation and enhancement of natural capital assets, reduction of environmental pollution, and growth in income and employment. These features, along with the ways of transition to a green economy and their benefits, challenges, and risks, are largely discussed in the paper [5-7]. It is noted that one of the essential elements in