This 4-day course introduces participants to the modelling of hydrochemical, isotope geochemical, and microbial processes with the popular PHREEQC and related software. Simulation of all major biogeochemical processes will be explained and practiced step-by-step starting from simple systems and going towards more complex integrated case studies in the end. The course is designed for people who want to refresh their knowledge on (isotope) hydrochemistry and learn how to construct (isotope) biogeochemical models for their own studies. The course focuses on applications in environmental chemistry and contaminant hydrogeology in groundwater and soils. Exercises cover both organic and inorganic (metal) biogeochemistry.