Multimedia environmental models are powerful tools for predicting the fate and distribution of chemicals in the environmental. They are used for assessing the potential exposure of ecosystems and humans to contaminants, as well as for developing and evaluating chemical management approaches. This workbook has been developed with the aim of providing support to students and researchers who are new to fugacity-based environmental modelling or wish to refresh their knowledge and skills. The nature and approach of fugacity-based calculations is developed methodically and sequentially from very first steps, with computational details explicitly shown and discussed. Whereas our text “Multimedia Environmental Models: The Fugacity Approach” gives detailed justification for the theoretical underpinnings of the fugacity approach, this workbook instead focusses on the step-by-step exposition of computational details and approaches without excessive theoretical justification. We believe that this approach will serve to help clarify the necessary computational steps and approaches needed to design and implement fugacity-based computations in real-life environmental contexts.