Recent discoveries of diamond and coesite in the upper crustal rocks of the Earth have drastically changed scientists' ideas concerning the limits of crustal metamorphism. This book provides detailed accounts of the discoveries of diamond and coesite in crustal rocks and provides insights regarding their formation at very high pressures. The formation of these minerals is related to subduction and continental collision and the tectonics, petrological and mineralogical conditions of diamond and coesite formation are each discussed. Written by the leading workers in this exciting field, this book attempts to define an entirely new field of metamorphism - ultrahigh pressure metamorphism (UHPM). In doing so, it explains the formation of ultrahigh pressure minerals and explores new ideas regarding the tectonic setting of this style of metamorphism. This book will be of particular interest to researchers and graduate students of metamorphic petrology and global tectonics.