This text (based on the opening keynote talk for CPOTE-2020) addresses the role of engineering thermodynamics in a world where mankind wishes to have access to low-cost energy. In practice, this implies a central role in the fine balance between economic growth, a risk of modern slavery, exploitation of the Earth's resources and global environmental problems such as climate change and scarcity of water, often leading to armed conflict. Clearly, the negative effects of all this may be alleviated a bit by selecting proper and low-cost energy sources and resources and using these as effectively as possible with zero or a minimum of negative side-effects. Engineering thermodynamics is an important tool here that can feed important information into the question: “How can things be done in a sustainable way (and make the world a better place)?" Thus, the sustainability of energy use will here be considered also from the viewpoints of the UN's seventeen Sustainable Development Goals (SDGs). Methods and tools for describing and optimizing energy use and energy-intensive processes and activities will be presented and mirrored against the use of available energy and material resources and the environmental footprint of that. This will give guidelines for how the scope must be widened to more multi-disciplinary evaluations and, in reverse, how engineering thermodynamics can be used as a tool for non-engineers and non-thermodynamicists, including decision-makers and politicians.