The second edition of 'Groundwater Geochemistry A practical guide to modeling of natural and contaminated aquatic systems' remains a comprehensive text book offering beginners and advanced modelers alike a minimum theoretical background and a strong focus on the practical solution of geochemical modeling with PHREEQC. The new edition covers the possibility of using the CD-MUSIC concept within the new version of PHREEQC. Examples for reactive transport use PHREEQC´s 1d features as well as the coupled 3d code PHAST with the graphical user interface WPHAST. Implementing uncertainties of thermodynamic data is addressed by means of the program LJUNGSKILE. As in the first edition, detailed descriptions on how to solve each problem guide the user step by step from basic to more and more advanced hydrogeochemical modeling.