Cyberbullying often occurs in group-based situations; therefore, how young people respond when they witness cyberbullying is important in the process of combating the issue. This study examined how young people perceive the severity of cyberbullying incidents and how they respond as a bystander according to different factors associated with cyberbullying (i.e., publicity, anonymity, type, and victim response). The final sample was 990 (545 female, 403 male, 42 non-disclosed) students aged between 11 and 20 years (Mage = 13.16, SDage = 2.14) from two schools and one college in England. Participants responded to 24 hypothetical vignettes which were manipulated to measure publicity, anonymity, type of cyberbullying, and victim response. Participants responded to items assessing a. perceived severity, and b. bystander responses. The bystander responses examined were: ignore the incident, encourage the bully, seek adult help, seek friend help, provide emotional support to the victim, and challenge the bully. Perceived severity was higher in public scenarios, when the bully was anonymous, and when the victim was upset. Victim response was the most influential factor across all response strategies on how young people react to cyberbullying, followed by the publicity of the incident, the anonymity of the bully, and to a limited extent, the type of cyberbullying. The results suggest that bystanders do respond differently to cyberbullying according to the publicity, anonymity, type of cyberbullying, and victim response.