generated across these various designs. Subsequently I review more conceptual issues surrounding the study of gene-environment interaction, covering the nature of gene-environment interaction effects as well as the challenges facing the study of gene-environment interaction, such as difficulties with differentiating various types of interactions, and how issues such as the scaling of environmental measures can have profound implications for studying gene-environment interaction. I include an overview of epigenet-ics, a relatively new area of study that provides a potential biological mechanism by which the environment can moderate gene expression and affect behavior. Finally, I conclude with recommendations for future directions and how we can take research on gene-environment interaction to the next level.
