<p>Universal parenting interventions for parents of adolescents are increasingly recognised as effective tools for promoting positive outcomes. This systematic review aimed to assess the effectiveness and retention rates of these interventions and compare various intervention characteristics. This systematic review follows PRISMA guidelines aiming to synthesise knowledge about universal parenting intervention. Quantitative studies of universal parenting interventions for parents of adolescents aged 11-21 were included. Data on intervention effectiveness, retention rates, and characteristics were extracted and synthesised narratively. 7,825 unique references were identified; 24 publications from 20 interventions met the inclusion criteria. Most interventions demonstrated effectiveness in improving targeted outcomes. Retention rates varied, with about half of the interventions achieving high retention (≥75%). Intervention characteristics associated with higher effectiveness included longer duration, more experienced facilitators, group delivery, and broader focus on family and school systems. Universal parenting interventions for parents of adolescents show promise in improving various outcomes. However, more research is needed on the specific components that contribute to effectiveness and retention. Future studies should focus on standardising outcome measures and reporting key intervention details to facilitate more robust comparisons and meta-analyses. Additionally, more research on organisational factors influencing these interventions in diverse educational and healthcare systems is needed.</p>