Earth-abundant iron and its oxides are not only "greener" than many of rare and precious metals, but can elegantly perform numerous catalytic reactions of industrial and environmental significance, often mimicking enzymes. Industrial applications include the use of iron and iron oxide-based compounds in pigments, magnetic recording media, catalysis, and magnetic fluids. Iron oxides have shown potential in manufacturing, water purification, and photocatalytic transformation to generate solar fuel. This book presents synthesis and application of ferrites, including high energy density rechargeable batteries, in cleaner ("greener") technologies for organic syntheses, and in environmentally friendly water and wastewater treatment processes. This book comprises 18 chapters with a focus on synthesis and environmental applications of ferrites and ferrates. Topics of the book encompass greener catalysis (nano-catalysis) emanating from ferrites and ferrates to achieve chemical energy transformation, organic syntheses and transformation, as well as eco-friendly water and wastewater treatment processes, namely removal of metals, oxidation of micropollutants, and inactivation of microorganisms and toxins.