The Ph.D. Thesis "Sustainable energy management in the life cycle of the hotel" deals with current issues of energy management in the hospitality and tourism industry. The research started from analysing the theoretical positions, regulations, standards and protocols that are applied in the EU and globally, as well as examples of good practice, and then the findings were connected with the results of the empirical research conducted on the selected sample of hotels in Croatia. The choice of the topic is based on the fact that tourism in Croatia is an extremely important industry, which must be developed according to the principles of sustainable development. However, as tourism is a significant polluter of the environment (the average hotel spends 39 TW/h of energy and emits about 10 tons of CO2 per room), where the use of fossil fuels stands out greatly with its negative impacts, this approach is supported by the knowledge that the hotel building is connected to the 40 % of total greenhouse gas emissions, primarily associated with the consumption of energy, and in the research the different ways were analysed as to how hotels can provide a cleaner and healthier hospitality and tourism environment, whilst reducing dependence on imported energy and, further, how the risks of climate change can be mitigated. With a detailed analysis of the results of the empirical study conducted, it was possible to analyse the types and methods of energy use in hotels, the achieved level of energy efficiency, all with the purpose of evaluating the real possibilities, economic and environmental assumptions of introducing renewable energy sources in Croatian hotels. Special emphasis is placed on the real possibilities of solar energy use, due to the high degree of insolation, especially on the coast and islands. The above benchmarks are elaborated in the form of the model, with the relevant instruments used, in order to prove that eco-investment in renewable energy sources are economically efficient and environmentally acceptable. With the positive effects of reducing the negative environmental impacts to tourist destinations, sustainable energy sources contribute to the sustainability of the hotel at all stages of its lifecycle. This contributes to the epithet of sustainable-hotel, which attracts the environmentally-minded guests of higher purchasing power, and ensures better working conditions for their employees. The conclusions that were obtained through a model of a seasonal hotel situated on an island tourist destination has a wider meaning, and can be accepted as a general-accepted framework, whose application may affect the reduction of greenhouse gas emissions and mitigating climate change. The implementation of these ideas in Croatian hotel practice, can contribute to the mitigation of energy dependence of Croatian fossil fuel imports. The value of the model is in the possibility of application of the relevant instruments, which takes into account the technical and economic facts, and whose application provides the information base for energy efficiency management in the hotel and beyond, based on the assessment of investment opportunities, costs rationalization and increasing efficiency and competitiveness, always following the principles of sustainability. All the proposed hypotheses are proven through the results of the empirical research and the development of the model.