This fourth edition of the book has been updated based on recent literature. It is still based on undergraduate and graduate courses I have taught for the past 45 years at the University of Miami. Over the past 10 years a number of new large-scale oceanographic programs have been initiated. This includes The Climate Variability Program and the recent initiation of the Geochemical Trace Metal Program. This program is aimed at understanding the biogeochemical cycles of trace elements in the oceans. The initial studies have already shown the input of Fe and Pb from hydrothermal vents and the redox behavior of metals in low oxygen waters. These recent and future studies will produce a wealth of information on the biogeochemistry of the world oceans. The increasing CO2 in the atmosphere from the burning of fossil fuels continues to affect the atmosphere and the oceans. The increased temperature of surface waters is causing stratification in the oceans. This has led to areas of low oxygen regions in coastal waters. Each year oceanographers contribute to the expanding knowledge of the oceans. I have tried to build and update this introduction to Chemical Oceanography with new understanding and concepts. The dissolution of C02 in the waters is lowering the pH. This lower pH will affect calcifiers in the oceans and biogeochemical processes such as equilibrium and rates of reactions. New research in the field of ocean acidification has been added as well as information on the new standards developed by the SCOR/IAPSO working group to describe the properties of seawater for researchers to report their measurements. Standardization of measurements in the literature leads to a clearer understanding and less confusion in reporting the processes in the oceans. More research will come over the next ten years and I will try to add any new and exciting changes in the oceans in my PowerPoint Lecture that I update each year. I hope the new edition covers some of the areas that were missing and gives a reasonable review of the basic concepts of the field.