This chapter focuses on a review of the pertinent literature examining the developmental manifestations of engagement in relational aggression across the life course, from infancy to old age. Throughout the chapter, special attention is paid to the normative developmental changes taking place in the various domains of development that are believed to underlie the significant alterations taking place in the expression of relational aggression. While the primary emphasis is on changes in relational aggression in the peer group, a review of important differences across contexts (e.g., school, work, etc.) and close relationships (siblings, friendships, romantic relationships, etc.) are also discussed, as are important technological advances that have helped shape the form of these behaviors at different points in development.