Book excerpt: Clay is an abundant naturally occurring raw material with different unique characteristics such as high surface area, chemical and mechanical stability, cation exchange ability, and more. This book is a comprehensive overview of clay science, covering the characterization and application of clay minerals. Applications such as stratigraphic correlation, environmental deposition indication, pharmaceutical uses, wastewater treatment, construction, and agriculture are explored. This book will provide an important reference for researchers, scientists and engineers who have a keen interest in clay as a sustainable material, solid acid adsorbent, and catalyst.