The use of sub- and supercritical (hydrothermal) water as reaction media and reactant provides a path for reducing the use of organic solvents. The technology can be integrated in industrial processing for safer, more flexible, economical, and ecological production in the context of green and sustainable engineering. This book covers a wide range of applications of hydrothermal processing that results in zero waste, high energy efficiency, zero toxicity, and minimal impact over life cycle. Applications include processing of hazardous waste, bioproducts, coal, lipids, heavy oil and bitumen, and carbon materials. The book details deep well reactor design and corrosion and salt precipitation.