Researchers have become increasingly interested in uncovering how genetic factors work together with the peer environment in influencing development. This article offers an overview of the state of knowledge. It first describes the different types of gene-environment correlations (rGE) and gene-environment interactions (GxE) that are of relevance for understanding the role of peer relations as well as the two main methodologies of genetically informed research, that is, the quantitative genetic approach and molecular genetics. This is followed by an overview of recent studies that examined different mechanisms of gene-environment interplay involving peer relations in childhood and adolescence. The article concludes with an outline of future directions in genetically informed peer relations research as well as the implications for theory and practice. (Contains 2 figures.)