There is rapid technological development in the world, especially in the fields of artificial intelligence, communication, and medicine. We need a great direct or indirect energy need for all these technologies, and the future of our planet is no more important than the invention of any technology. The pandemic we are experiencing due to the Covid-19 virus mercilessly confirms this. In the last century, we have rapidly harnessed and almost exhausted the oil, coal, and natural gas reserves that need millions of years for nature to create. Using these limited reserves is not sustainable. As we consume these fossil fuels mostly by burning, we have suffered great climatic damage and the lack of unsustainable fossil fuels necessitates sustainable energy research. We need a sustainable environment and sustainable energy resources to make life sustainable. The social cost of climate change caused by fossil fuels is many times higher than the cost of preventing climate change. However, the damage caused by climate change cannot be compensated for most of the time. In other words, getting rid of fossil resources will be the most effective method in meeting the energy demand of human beings. There are still many power plants in the world where fossil fuels are used. In addition, considering the fossil fuels consumed in buildings and vehicles, the magnitude of the problem becomes more evident. However, the transition to 100% carbon-free energy requires a unique engineering effort. Although the ultimate goal of scientists is to achieve sustainability with 100% carbon-free energy, this will of course not be easy. In addition to the environmental factor of sustainability, a solution must be produced by taking into account the economic, social, and sociological factors. This book includes original scientific studies of scientists in different disciplines, in which these factors are evaluated separately. Because sustainability concerns not only energy but all areas of life and therefore it can be used as a common keyword for all engineering fields. Let's not forget that the future belongs to all of us, and as we protect nature, nature will protect us.