In everyday life, adolescents’ authenticity and inauthenticity (sense of, and being, the real me/true self; or false self/not the real me) are assumed to be general indicators of their psychosocial health as they navigate developmental processes of identity exploration and relational connectedness on their way to adulthood. Authenticity is important for psychological thriving in adolescents and inauthenticity is considered maladaptive, but there was no broad and systematic evidence-based resource on the topic. Therefore, this scoping review maps: (1) how authenticity and inauthenticity in adolescents (12–18 years old) have been understood, defined, and characterized; (2) what is known about authenticity and inauthenticity; (3) contexts authenticity and inauthenticity have been explored in; and (4) methodological approaches utilized. This review followed a pre-registered protocol (2852 records identified; 39 peer-reviewed primary research studies included). The review revealed authenticity and inauthenticity are typically: characterized as dispositional, involving thoughts, feelings, awareness, and a sense of being one’s true self or a false self; investigated quantitatively; and contextualized in close social relationships (parents, friends, classmates). Authenticity and inauthenticity outcomes included friendship quality, wellbeing, self-esteem, depressive symptoms, internet addiction, and moral disengagement. Adolescents’ authenticity generally increases over time and social support is very important for that process. Adolescents can be more authentic if parents facilitate adolescents’ increasing independence and support role experimentation. Future research should target state (here-and-now) authenticity, as a critical finding was that autonomy satisfaction has an immediate and positive influence on adolescents’ state authenticity, which implies people interacting with adolescents can promptly boost their capacity for positive psychological development.