The purpose of this course is to introduce students to conceptual issues and analytical approaches to assess causal mediation effects under observational study designs. At the completion of the course students should have developed an understanding of formulating research questions in causal terms, the merits of different statistical approaches to assess mediation, and the theoretical and statistical assumptions behind these approaches. In turn, they will be able to determine the most appropriate approach to assessing mediation, given their data source, available measures and research question.