1 THE CHALLENGING PARADIGM OF INTERRELATED ENERGY SYSTEMS TOWARDS A MORE SUSTAINABLE FUTURE N. Soares a,b,c , A.G. Martins c,d , A.L. Carvalho e , C. Caldeira a,c , C. Du a,c , É. Castanheira a,c , E. Rodrigues a,c , G. Oliveira c,f , G.I. Pereira c,f,g , J. Bastos a,c , J.P. Ferreira h , L.A. Ribeiro f,i , N.C. Figueiredo c,f , N. Šahović c,f , P. Miguel c,f , R. Garcia a,c a ADAI, LAETA, Department of Mechanical Engineering, University of Coimbra, Pólo II, Rua Luís Reis Santos, 3030-788 Coimbra, Portugal b ISISE, Department of Civil Engineering, University of Coimbra, Pólo II, Rua Luís Reis Santos, 3030-788 Coimbra, Portugal c Energy for Sustainability Initiative, University of Coimbra, Pólo II, Coimbra, Portugal d INESC Coimbra, Department of Electrical and Computer Engineering, University of Coimbra, Rua Sílvio Lima, Pólo II, 3030-290 Coimbra, Portugal e Federal Institute of Mato Grosso, Campus Diamantino, Rodovia Roberto Campos, 78400-970 Diamantino, Brazil f INESC Coimbra, Rua Sílvio Lima, Pólo II, 3030-290 Coimbra, Portugal g MIT Portugal Program in Sustainable Energy Systems, Massachusetts Institute of Technology, 77 Massachusetts Avenue, E18-430, Cambridge, MA 02139, USA h GOVCOPP, Faculty of Economics, University of Coimbra, Av. Dias da Silva, 165, 3004-512 Coimbra, Portugal i Postgraduate Program in Architecture and Urbanism of the Polytechnic School at Faculdade Meridional (IMED), Passo Fundo, Brazil Abstract This paper brings together several contemporary topics in energy systems aiming to provide a literature review based reflection on how several interrelated energy systems can contribute together to a more sustainable world. Some directions are discussed, such as the improvement of the energy efficiency and environmental performance of the systems, the development of new technologies, the increase of the use of renewable energy sources, the promotion of holistic and multidisciplinary studies, and the implementation of new management rules and "eco-friendly and sustainable" oriented policies at different scales. The interrelations of the diverse energy systems are also discussed in order to address their main social-economic-environmental impacts. The subjects covered include the assessment of the electricity market and its main players (demand, supply, distribution), the evaluation of some urban systems (buildings, transportation, commuting), the analysis of the implementation of renewable energy cooperatives, the discussion of the diffusion of the electric vehicle and the importance of new bioenergy systems. This paper also presents relevant research carried out in the framework of both the Energy for Sustainability Initiative of the University of Coimbra and the Sustainable Energy Systems focus area of the MIT-Portugal Program. To conclude, several research topics that should be addressed in the near future are proposed. Keywords Electricity markets, Electricity distribution, Industrial ecology tools, Urban planning, Electric vehicle, Bioenergy systems