Teen dating violence victimization is associated with a host of adverse mental and physical health problems. A number of bystander-focused interventions have been developed to mitigate the occurrence of abuse but with varying effectiveness. There remains a need to understand more about bystander behaviors used by adolescents to ensure that existing intervention components match with bystanders' attitudes and behaviors about intervening. The current study is a scoping review of existing literature on adolescents' use of bystander behaviors to determine "who," "when," "how," and "why" adolescents intervene. Seventeen articles met inclusion criteria, the majority of which used qualitative or observational survey designs. Adolescents "who" either feel a sense of responsibility and confidence to intervene or are directly involved with or know the individuals involved in the abuse are more likely to intervene. Adolescents intervene "when" they are able to define an act as abuse and tend to intervene when the victim is female and when they have a supportive relationship with at least one teacher in their school. The various ways "how" bystander intervention is engaged in ranges from verbally or physically confronting the abuser, distracting the abuser, seeking support from an adult, to passively accepting the abuse. Reasons "why" adolescents intervene include believing the abuse is wrong and that intervening will diffuse the situation and help the victim. A number of barriers to bystander intervention emerged from analysis, including individual attitudes and school climate factors. Implications for strengthening bystander intervention programs are discussed. [This paper was published in "Trauma, Violence, & Abuse" v22 n1 p54-67 2021.]