This book provides a concise and in-depth overview of clay minerals. Clay is a versatile material which has varied applications depending upon its properties and composition. Clay minerals are inexpensive and sufficiently available on earth. They have 1 nm silicate layers in almost all the sediments and are eco-friendly because they are natural minerals. This book discusses basic properties and role of clay minerals in deposits. It also deals with the importance of clay in the soils. This book also covers various aspects of research in this domain, especially to the identification of clay structure and its alteration for different applications.