Early life stress (ELS) and abuse are the most commonly assessed environmental exposures in psychiatric genes and environment (GxE) interaction studies, partly because of the strength of evidence that ELS plays a role in risk for multiple psychiatric disorders. The research on GxE interactions is organized by the presumed underlying neurobiological systems and by the broader classification of psychiatric outcomes (mood/anxiety disorders and externalizing disorders). This chapter discusses the importance of clearly defining and measuring both the proposed environmental risk/resilience factors as well as the predicted diagnostic and behavioral outcomes. This allows investigators to conduct GxE studies that better inform the understanding of the role of ELS in predicting psychiatric risk/resilience. The chapter focuses on childhood physical, sexual and emotional abuse, which is currently among the most well-researched environmental risk variables in human psychopathology research.