Using data from a sample of 218 high school youth from three high schools in New England (one rural, two urban), this brief discusses dating and sexual aggression bystander intervention among high school youth. Authors Katie Edwards, Robert Eckstein, and Kara Anne Rodenhizer-Stämpfli report that an overwhelming majority (93.6 percent) of high school students reported having the opportunity to intervene during the past year in situations of dating aggression or sexual aggression; however, in over one-third of the episodes (37.4 percent) students reported not intervening. Girls were more likely to intervene in situations of dating and sexual aggression than boys, and youth with histories of dating and sexual aggression were more likely to intervene than youth without these histories. Focus group data revealed that barriers to bystander intervention included avoidance of drama or a desire to fuel drama, social status and personal repercussions, closeness with the victim and/or perpetrator, the victim being male and the perpetrator female, the failure of the dating or sexual aggression to meet a certain threshold, the dating and sexual aggression occurring online, anticipated negative reactions from the perpetrator or victim, and an inability to relate to the situation. Given the mounting evidence that bystander education is a critical component of dat­ing and sexual aggression prevention, the authors urge policy makers and educators to enhance the presence of this type of education in high school health curricula and related course curricula. [Funding for this project was provided collectively by the University of New Hampshire's Carsey School, the Prevention Innovations Research Center, and the College of Liberal Arts Dean's Office.]