The goal of this workshop is to present key methodological challenges that arise when assessing mediation or decomposing causal effects into direct and indirect components, and to provide an overview of the different methods that can be used to deal with these challenges. We will also present concrete examples applied to environmental epidemiology with Stata software. At the end of the workshop, participants will be aware of modern epidemiologic methods to study mediation processes in environmental epidemiology, correctly interpret software outputs and have the requisite skills to conduct mediation analysis in their own research projects. The workshop will be organized into 2 parts: In the first part, Jay S Kaufman, Lorenzo Richiardi and Rino Bellocco will give a 90 minute lecture about mediation analysis in environmental epidemiology presenting assumptions, interpretations and an overview of the different modern methods to conduct mediation analysis. In the second part, Tarik Benmarhnia and Payam Dadvand will present during 90 minutes concrete examples using the software Stata and applying the methods presented in the first part of the workshop. These examples will be related to different environmental exposures such as air pollution, green spaces or heat waves.