These slides were presented as part of the Division of Biostatistics and Epidemiology, Causal Inference Research Interest Group seminar series. Topics covered in this talk include an introduction to Directed Acyclic Graphs (DAGs), why and how use DAGs, DAG terminology, limitations of DAGs, and several case studies. While these slides are not so recent, I decided to post them here anyway in the hopes they might of use to others since I discuss this topic with collaborating investigators often.