Research on bullying is a relatively new field dating back to the early 1970s. It is characterized by a consensual definitional practice rooted in positivist psychology. However, since the turn of the twenty-first century, a social turn has introduced a broader range of theoretical frameworks and methodologies to the field. This development is inspiration from adjacent disciplines and fields, as well as by demands for more nuanced forms of knowledge that better reflect the issues facing practitioners. The entry takes the reader from the first studies of bullying as a group phenomenon, through positivist psychology’s decades-long dominance of the field, before exploring the social turn that began around the turn of the twenty-first century. UNESCO’s involvement in establishing a social and more inclusive definition of bullying in the early 2020s is described before the entry concludes by highlighting some of the challenges facing contemporary research on bullying.