Energy can be converted into a useful form by letting miscible fluids of different compositions mix with each other. A major natural source for such a process is the earth"s river and ocean water resources. For example, mixing 1 m3/s of river water and 1 m3/s of ocean water could theoretically supply 1.6 MW of power. This process of mixing river and ocean water would provide renewable, permanent, and practically waste-free power production. An alternative source is provided by concentrated industrial brines. Despite the great potential, energy conversion from mixing species is not yet an economically viable energy conversion method. This book consists of theoretical and experimental studies on osmotic flows and their future application for energy conversion.