"Introduction to Clay Minerals" is designed to give a detailed, concise and clear introduction to clay mineralogy. Using the information presented here, one should be able to understand clays and their mineralogy, their uses and importance in modern life. The study of clay minerals has been very active in the past four decades. However, there have been as yet few attempts in the past 20 years to unify the great store of knowledge concerning hte chemistry, origin, uses and role in the geologic domain of these fine particles. The interaction of living and mineral world is most often governed by clay chemistry: soils, sediments and sedimentary rocks are the keys to present-day environmental problems. The methods used to identify and characterize clay mineras, as well as their chief chemical and crystallographic characteristics, are outlined in this work. These two types of information are inter-related because the response of an analysis mehtods is always partial and spcific to a given part of mineral structure. X-ray diffraction, infrared, electron microscopy, DTA and other methods give details concerning one or another part of aspect of a clay mineral. In order to understand the methods one must understand the basics of the structure and chemistry of a mineral. These are given in detail in the text. It demonstrates that clay mineralogy is not complicated and can be generalized into several basic mineral families for which a small number of variables determine their roles in geology and their physical-chemical properties. The origins of clays are stressed because they demonstrate the main geological situation and interaction of clay minerals. The geology of clays is fundamental to the concept of thei environmental impact. "Introduction to Clay Minerals" is designed to be read, either as a beginning text for clay mineralogists or as a supplementary text in courses on agronomy, environmental science, and related fields. It should have a wide audience at many different levels of education and professional use, in universities, agronomy institutions and in industry.