The first edition of Geochemistry, groundwater and pollution has become a popular textbook that is used throughout the world in university courses and as a reference text. The new developments in our science during the last decade have inspired us to update the book. There are now more data available, more experiments have been done, new tools were developed, and of course, new problems emerged. An important catalyst for rewriting the book was the advancement of the computer code PHREEQC. From the start in 1980, this model was developed to simulate field data and laboratory experiments and at present it encompasses over 20 years of experience in modeling water quality. The code is used all over the world in research and to predict the long-term effects of pollution and radioactive waste storage. Modeling with PHREEQC is an integrated part of the presentation in the second edition. It is used to elucidate chemical concepts when they become complicated and in particular to analyze the interactions between chemical processes and transport. Numerous examples in this book show PHREEQC applications with input files listed in the text. The more comprehensive ones can be downloaded from the net and are useful templates for similar problems.