This vision article accompanies a special issue of Applied Thermal Engineering dedicated to the 16th Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES) held in Dubrovnik in 2021, and summarizes a selection of papers presented at the conference. At the focal point are a range of topics related to thermal processes as these arise in energy production, storage, utilization and conservation, covering fundamental research, the development of technical solutions for diverse sustainable engineering applications, technoeconomic analyses, and issues relating to the potential and integration of technologies from higher-level approaches. Thermal processes are the basis of numerous sustainable engineering applications and their understanding and improvement are increasingly required in the context of improved resource use efficiency and reduced environmental impact. Applications of interest include thermal systems used in buildings, thermochemical processes, seawater treatment, thermal storage solutions and renewable energy resource use. Emerging challenges in this space have given an opportunity to scientists, researchers and engineers to actively contribute to the development of relevant technological solutions, which are covered briefly in the present article.