Kritz, Marlene ORCID: https://orcid.org/0000-0002-4706-4891, Riddell, Hugh ORCID: https://orcid.org/0000-0001-8218-7822, Olsen, Daryn, Harden, Samantha M., Burke, Shauna M. ORCID: https://orcid.org/0000-0003-2749-1631, Ntoumanis, Nikos and Thøgersen-Ntoumani, Cecilie ORCID: https://orcid.org/0000-0003-0255-1263 (2026) Individual versus group-based interventions: a systematic review and meta-analysis of physical activity, functional, psychosocial and health outcomes. Nature Human Behaviour.