Bias-based harassment has emerged as a significant concern in schools globally. Unsurprisingly, exposure to such negative treatment has detrimental effects on the psychological functioning, academic performance, and behavioural adjustment of children and adolescents. Thus, there is a pressing need to develop a comprehensive understanding of the factors that exacerbate or mitigate the negative consequences of bias-based harassment on its victims, as well as the factors that lead young people to engage in bias-based harassment. To address this need, this paper begins by providing a brief overview of the literature on bias-based harassment and bullying among early adolescents and adolescents. Subsequently, we introduce the studies featured in this special issue and present an integrated summary of their key findings. Our goal with this special issue is to compile scientific evidence on this social concern across diverse school settings and pave the way for future initiatives aimed at addressing bias-based harassment more comprehensively and efficiently.