Background: Adoption of more sustainable diets is necessary to preserve human and planetary health. The reach of the school meal system makes it an ideal setting to focus a food-related intervention towards more sustainable meals. The motivation to shift to more sustainable eating is increasing in the younger generation. However, there is currently limited insight into why and how these preferences develop and can be promoted. Aim: To explore barriers and facilitators to implementing sustainable school meals in the Swedish high school setting. Methods: This study employed a mixed inductive-deductive qualitative design. Interviews with high school students (n=16) and school kitchen staff (n=3) were conducted and transcribed verbatim. Data was first analysed inductively using qualitative content analysis. Emerging barriers and facilitators were consequently mapped deductively onto the domains of the Consolidated Framework of Implementation Research (CFIR).Results: Ten barriers and seven facilitators to implementing more sustainable high school meals emerged. These belonged to two domains of the CFIR: individual characteristics of students and kitchen staff and inner setting factors such as school meal environment and relationships between stakeholders. Barriers included a low desirability toward vegetarian meals as well as lack of knowledge on the nutritional value of plant-based proteins among students. A barrier for the meal staff was that they were less inclined to prepare more plant-based meals which were perceived as less acceptable among students. Facilitators included a common interest in change towards sustainable meals and a good relationship between students and meal staff. Also, kitchen staff perceived that they have the knowledge and resources necessary to implement change. Conclusion: Prioritizing students’ food preferences as well as their knowledge about food and sustainability is likely to be key, but possible not enough, to achieve successful implementation of sustainable school meals. Co-creation with consumers and providers could provide an important opportunity to reaching higher acceptability of new meals and thus avoiding food waste.