This chapter outlines what is known about the characteristics, vulnerabilities, and on- and offline behaviour of victims of online-facilitated child sexual abuse and exploitation, considering the analysis carried out through a systematic rapid evidence assessment (REA). Beginning with a summary of research sources, it presents four general conclusions from the research. First, online child sexual victimisation (OCSV) is varied. At least five types of OCSV were identified: grooming by strangers, primarily initiated in social networking or gaming websites; sexual exploitation by strangers in webcam centres and similar; sexual abuse by family members or acquaintances that is photographed or videoed; coercive sexual violence between peers, leading to youth-produced material; and trafficking of child abuse material online. Second, an important finding from the triangulation of the different data sources is the under-reporting, and lack of research, concerning young children who are subject to OCSV. A third finding is that the field encompasses a wide range of behaviours and social phenomena that are often implicit in the research, including the relationship between sexual victimisation and other sources of harm, such as cyberbullying; childhood sexual activity that is not violent; gender regimes and patriarchy; and social divisions and intersectionality. Finally, there is significant variation in the definitions and concepts utilised in the research, which makes direct comparison problematic.