In a global perspective, it is essential that the world transfers from fossil fuels to renewable energy sources in order to minimise climate change effects. As a part of such transition energy savings are also important, as they can decrease production costs effectively. The nature of such a change is that it has to be implemented on a local level. Energy saving technologies are placed with the demand decrease and renewable energy is typically distributed where the resources are. In some parts of the world, energy savings have resulted in a stabilisation of the energy demands, however in the world as such, demands are still increasing in buildings, transport and industry. Although the demand has increased approx. 32% overall, the share of renewable energy has increased from 12.7% in 1990 to 13% in 2010, in this way demonstrating that renewables can effectively cope with the world energy requirements – even in a context characterized by a continuously increasing demand. Even in the current financial crisis, renewable energy is expanding heavily . The most used renewable energy is biomass; however there has been a significant increase in wind power and in photovoltaic in the last ten years. Such development in the intermittent renewable energy sources requires knowledge about the interaction between supply and demand sides of energy. At the 6th Dubrovnik Conference on Sustainable Development of Energy, Water and Environmental Systems, September 25–29 2011, in Dubrovnik, Croatia, these issues were addressed among others. The conference was dedicated to research concerning methods, policies and technologies for increasing the sustainable development as well as methods for assessing and measuring sustainability of development, regarding energy, transport, water and environment systems and their many combinations. At the conference 418 scientists from 55 countries representing six continents participated. In this Special Issue the interaction between sectors and renewable energy systems through selected papers from this conference is addressed from a range of technical system analyses to environmental and economic feasibility.