Two university professors in Earth Science have dedicated their life of teaching and research to the keywords: Rock deformation and Tectonics . Plate displacements on Earth, such as the opening of the Atlantic Ocean or the northward Indian drift since 45 million years, are based on deformation of the rocks, hence of the minerals that make them. The understanding of their mechanisms is the heart of this book. Knowing that the continents, principally made quartz and feldspars, differ from the mantle which is dominated by olivine in composition, this book explains the interplay between the tectonic forces (or stress) applied to rocks, and the results (or strain) suffered by them. Explanation is givens step by step as a function rock types and temperature, hence depth. This book also gives some keys for the measurement of the horizontal and vertical displacements and their rates, and describes the main tools commonly used in modern Earth Science applied to tectonic studies.