The book introduces the Tsallis entropy theory to the water engineering community. Due to versatility of the theory and its potential applications (already extensively applied in physics and chemistry), it will help with teaching and research in hydrology, hydraulics, and water resources engineering- and more applications of the theory are emerging each year. The book will deal with basic concepts of this theory from a water engineering perspective and applications of these concepts to a range of water engineering problems. It will also provide a number of solved examples to illustrate the concepts presented.