This monograph has been prepared to serve as a basic reference for both the field and research engineer interested in developing a fundamental understanding of the acidizing process and procedures for designing acid treatments to increase well productivity. Accordingly, we have attempted to structure the monograph to serve both groups. Some chapters provide a comprehensive review of the science and technology that serve as bases for understanding the fundamentals of acid stimulation. Others are written for the field engineer and stress design procedures and the proper selection of fluids and additives. These procedures employ practices in wide-spread use in the United States and, to a lesser extent, in use throughout the free world.