This book treats cavitation, which is a unique phenomenon in the field of hyd- dynamics, although it can occur in any hydraulic machinery such as pumps, propellers, artificial hearts, and so forth. Cavitation is generated not only in water, but also in any kind of fluid, such as liquid hydrogen. The generation of cavitation can cause severe damage in hydraulic machinery. Therefore, the prevention of cavitation is an important concern for designers of hydraulic machinery. On the contrary, there is great potential to utilize cavitation in various important applications, such as environmental protection. There have been several books published on cavitation, including one by the same authors. This book differs from those previous ones, in that it is both more physical and more theoretical. Any theoretical explanation of the cavitation phenomenon is rather difficult, but the authors have succeeded in explaining it very well, and a reader can follow the equations easily. It is an advantagein reading this book to have some understanding of the physics of cavitation. Therefore, this book is not an introductory text, but a book for more advanced study. However, this does not mean that this book is too difficult for a beginner, because it explains the cavitation phenomenon using many figures. Therefore, even a beginner on cavitation can read and can understand what cavitation is. If the student studies through this book (with patience), he or she can become an expert on the physics of cavitation.