Recognizing adolescence as a period that holds both opportunities and risks, this study tested whether adolescents in Israel flourish, as defined by the ability to attain high levels of well-being. The study’s main aims were to identify components and processes that enable Israeli adolescents to flourish versus those linked to low levels of flourishing. A convenience sample was comprised of 917 adolescents, age 14–18 (M = 16.13, SD = 0.97), including 599 females and 318 males; 582 were Palestinian Israeli and 335 were Jewish Israeli. Native-tongue questionnaires (in Arabic/Hebrew) assessed: peer and family social support and social undermining (Social Support and Undermining Scale); positive and negative affect (PANAS); and the three subscales of flourishing: emotional, social, and psychological (Mental Health Continuum-Short Form). Using structural equation modeling, the main findings revealed that positive affect mediated the link between supportive resources (by family and peers) and adolescents’ flourishing, while negative affect mediated the link between social undermining (by family and peers) and adolescents’ low levels of flourishing. The same pattern emerged in both cultures, although with full mediation for the Palestinian Israeli group and only partial mediation for the Jewish group. Findings emphasized both social support and positive affect as having implications in designing preventive and treatment programs that target individual adolescents and their families.