**Anotation** Acceptance and Commitment Training (ACT) aims to build and strengthen psychological flexibility processes among athletes and improve their performance, well-being, and mental health. Meta-analyses and systematic reviews show that acceptance-based and mindfulness-based interventions might be effective in achieving these goals (Bühlemayer et al., 2017; Noetel et al., 2019; Ptáček et al., 2023), but none of the meta-analyses, or systematic reviews differentiate the developmental phases of participants within included studies. Youth athletes' context undoubtedly differs from adult athletes. When using contextual-based approaches (such as ACT) with youth, practitioners must consider contextual and developmental factors (i.e., metacognition and language, identity development, cultural influences, social dynamics, and others). In this regard, we argue that the evidence base of ACT among adult athletes cannot be used to guide practitioners working with youth. At the same time, youth athletes make up a substantial part of the population of competitive athletes facing the pressure of known demands of the sporting environment. Thus, there is a need to differentiate the evidence base based on the developmental phases of athletes. --- **Aim of the project** Firstly, we aim to assess current research on ACT within youth sports through a systematic review. Additionally, we aim to develop an online training program for adolescent athletes, which can inspire sport psychology practitioners working with youth to create time and space flexible and affordable alternatives to face-to-face mental training. --- **Research and expert team** Mgr. Martin Ptáček (Department of Psychology, Faculty of Arts, Masaryk University) Ricardo Gregorio Lugo, Ph.D. (Department of Welfare, Management and Organization, Faculty of Health, Welfare and Organization, Østfold University College) doc. PhDr. Martin Jelínek, Ph.D. (Department of Psychology, Faculty of Arts, Masaryk University) doc. PhDr. Iva Burešová, Ph.D. (Department of Psychology, Faculty of Arts, Masaryk University) PhDr. Kateřina Koros Bartošová, Ph.D. (Department of Psychology, Faculty of Arts, Masaryk University) Anders Dechsling (Department of Education, ICT and Learning, Faculty of Teacher Education and Languages, Østfold University College) --- **Video Production Team** Mgr. Irina Matusevič (Centre for Information Technologies, Faculty of Arts, Masaryk University) Bc. Benedikt Kyselka (Centre for Information Technologies, Faculty of Arts, Masaryk University) Bc. Martin Ingr (Centre for Information Technologies, Faculty of Arts, Masaryk University) --- **Funding** The project is a bilateral initiative funded by the Fund for Bilateral Relations under the EEA and Norway Grants (EHP-BFNU-OVNKM-4-127-2023). ![enter image description here][1] [1]: https://mfr.osf.io/export?url=https://osf.io/download/hcbmv/?direct=&mode=render&format=2400x2400.jpeg