This book is about metamorphic rocks: the processes involved in their formation and the reasons why they occur at particular places on the continents. It has been written to serve as an elementary text on the subjects of metamorphism and mountain building for non-specialist stu dents of geology. It will be equally useful where geology is either the main or subsidiary subject and could be used by students intending to advance further in geology (the list of advanced texts in the further reading section would be more appropriate to such students). My inten tion in writing this book has been to try to dispel the notion that metamorphism comprises the 'haunted wing' of geology. Admittedly, there are rather a large number of technical terms in the book, but I hope that after working through it you will not find metamorphism an unduly difficult or obscure aspect of geology. Throughout, I have emphasised the strong links between mountain building, plate tectonics and metamorphic processes. The book introduces metamorphic rocks by considering their textures and field relations, then moves on to deal with the factors controlling metamorphism. Case studies of areas of metamorphic rocks are then presented in the context of modern theories of the Earth's activity, and the place of metamorphic rocks in the formation of ancient and young mountain belts is analysed. New technical terms and concepts are explained in context as they are introduced, important terms being emphasised in bold print.