This book guides the reader through a territory of applied photochemistry of iron compounds, and unveils its domains and importance. It provides basic information and numerous examples of the involvement of iron compounds in photocatalytic degradation of harmful substances such as pesticides, dyes, and microorganisms in all parts of the environment, i.e. soil, aquatic media and air exploiting advanced oxidation processes. It gives information on the involvement of iron compounds in polymer photochemistry, mainly in photopolymerization, photostabilization and photodegradation of polymers. A due space is reserved for photomagnetic phenomena, such as light-induced spin crossover phenomena, photoaggregation, changes in magnetic behaviour due to optically induced electron transfer, as well as magnetic field impact on excited states. It describes situation in sea-waters related photochemistry. Important part of the book is devoted to photochemical synthesis of iron compounds and their catalytic role in photochemical synthesis of organic compounds. The book represents a suitable document both for those starting and involved in the field, as well as university students.