The Fourth Edition of Soil Chemistry has been thoroughly revised and updated to reflect the latest concepts and developments in this field. Thoroughly reorganized for ease of use, this updated Fourth Edition provides a comprehensive yet accessible overview of latest research in this area and fundamental knowledge in the field in a single text. The main objectives for the revision of Soil Chemistry are : 1) updating concepts, 2) modernizing figures and layout, and 3) bringing more focus. 1. Updating Concepts: The current text presents the fundamentals of soil chemistry, which have not drastically changed since the first edition.  However, over the decades, the discipline of soil chemistry has changed to include more environmental science, and less agricultural science.  The fourth edition will include modern examples of environmental soil chemistry, yet maintain a balance of examples from agricultural chemistry.  In fact, many agricultural issues and environmental issues are one and the same.  Current soil chemistry challenges for society are: excess nutrient leaching to surface and ground water, C cycling, soil contributions to GHG, agricultural waste management, pesticide management, irrigation leaching of contaminants, Hg contamination, organic matter stabilization, black carbon in soils,  nanoparticles, virus and microbe interactions with minerals, and organic/sustainable agriculture.  In addition, the hallmarks of soil chemistry are still relevant: nutrient use efficiency, mineral weathering, soil pollution, soil acidification, particle-particle interaction, and soil salinity.  In the fourth edition, the principles of soil chemistry will continue to be the emphasis, but examples from current topics will be interwoven to provide relevance and demonstrate soil chemical processes. 2. Modernizing figures and layout.  The objective here is to provide more approachable learning content and formatting.  In the fourth edition we will enhance the material presentation by including better graphics and pictures (color where necessary), and learning modules or topic boxes.  For example, the topic boxes will include case studies that demonstrate chapter topics and show application of concepts, or real world examples of chemical reactions and calculations.  These learning modules will be offset from the main text.  Examples will be carefully selected such that they will maintain relevance for the anticipated life-cycle of the text. 3. Enhanced focus.  In the fourth edition, the level of information will be maintained so that the content can be covered in a semester-long course.  In the third addition, appendices were increased to cover details.  In the fourth edition, we will reduce, but not eliminate, appendices.  This will be achieved by eliminating some information in the appendices, incorporate them in main text where possible, and adding references to other texts or review articles for further reading on topics.  Additionally, some of the material in the appendices will be included in the learning modules. The original authorship will be maintained, although Dr. McNeal is not available to work on the text, and Dr. Strawn will be added as fourth author.  The new text will be modernized so that it can continue to fill the niche of previous versions as a readable and approachable text for a one-semester long undergraduate course.  It is the authors intention that the text will help attract non-major students to soil science and soil chemistry, which has great relevance for todays natural resource management challenges.