Cavitation is a phenomenon that commonly occurs in many areas of technology. It accompanies liquids flowing in channels of characteristically variable geometry. There are cases when cavitation effects are undesirable as they may cause damage to fluid-flow subassemblies of machines and devices. On the other hand, in environmental protection technology cavitation effects appear to be very useful in supporting chemical processes, in particular when applied in technologies of treatment/decomposition of substances that are harmful for humans and their immediate environment. Containing the state-of-the-art in hydrodynamic cavitation, the book consists of two parts. The first one presents the physical basis of cavitation , and a systematic classification of various kinds of cavitation and their formation sources. Special attention is paid to a group of factors that promote cavitation formation in natural liquids. A general model of cavitation is formulated as well as a sub-model describing dynamics of the formation, development and collapse of cavitation bubbles. The sub-model also includes effects of cavitation bubble occurrence on the liquid in the direct vicinity of bubbles. Finally, part one also includes a thermodynamic hydrocavitation model of water containing cavitation nuclei (natural waters). The second part deals with the application of hydrodynamic cavitation effects to advanced oxidation of substances that pollute the natural environment. Results of laboratory experiments on the application of cavitation effects to decompose selected organic compounds which hardly undergo biodegradation are presented, as well as a concept of the cavitation phenomenon application on an industrial scale. Application of Hydrodynamic Cavitation in Environmental Engineering will be useful to professionals dealing with the design and practical application of hydrocavitation reactors, and to academics in environmental engineering.