There has been a great advance in the understanding of processes of meta­ morphism and of metamorphic rocks since the last edition of this book appeared. Methods for determining temperatures and pressures have become almost routine, and there is a wide appreciation that there is not a single temperature and pressure of metamorphism, but that rocks may preserve, in their minerals, chemistry and textures, traces of their history of burial, heating, deformation and permeation by fluids. However, this excit­ ing new knowledge is still often difficult for non-specialists to understand, and this book, like the first edition, aims at enlightenment. I have concen­ trated on the interpretation of the plate tectonic settings of metamorphism, rather than following a geochemical approach. Although there is an impress­ ive degree of agreement between the two, I believe that attempting to discover the tectonic conditions accompanying rock recrystallization will more readily arouse the interest of the beginner. I have used a series of case histories, as in the first edition, drawing on my own direct experience as far as possible. This m~ns that some subjects are treated in more detail than others, and many important topics are barely mentioned at all. It also means that general concepts appear in a rather haphazard order in the text. To help my readers, I have provided a glossary of definitions of terms used in the book, which are indicated in bold type in the text.