This book describes the developments leading to the Original Cam Clay model, focusing on fundamentals of the shearing of soil. The aim is to lay the groundwork of understanding that should form the basis of geotechnical design, guiding engineers towards the class of behaviour to be expected under different combinations of effective stress and water content. In this book there are a few equations, but simple ones; much greater challenge rests in the arguments put forward regarding soil behaviour and the intellectual effort needed to keep pace with the author.