Young people are recognised as critical stakeholders in environmental governance, yet their involvement in decision-making remains limited. As the climate and biodiversity crises intensify, ensuring meaningful youth participation is essential for fostering inclusive and future-oriented environmental governance. This scoping review examines the literature to understand the “where, who and why” of youth involvement in environmental decision-making. Our findings reveal an imbalance of literature emerging from Global North institutions, despite studies focusing on Global South contexts, highlighting the need for greater research led by scholars and institutions in the Global South to better reflect local priorities, contexts, and epistemologies in youth engagement. We uncover wide variation in the age ranges considered as youth coupled with a lack of justifications behind them, revealing conceptual and methodological vagueness. Our research reveals a dominance of rights-based rationales for engaging young people (e.g. intergenerational justice and impacts of climate change disproportionately affecting young people) compared to strategic ones (better policy outcomes, young people’s creativity and innovative thinking). There is an urgent need for those involved in youth research and practice to be transparent regarding who they are engaging with, why engagement is happening, and the consequences of this. Overall, we call for future youth research and engagement to challenge the limited and blurry conceptualisations of who counts as a young person, and to embark on youth work that is transparent, reflexive, intentional, and balanced with youth input at the forefront.