Background: Capacity building and community-level participation are important to enhance the efficiency and sustainability of health promotion programmes, as well as to promote empowerment and decision-making power. However, stakeholders’ participation in the design and implementation of health promotion projects often involves the provision of information and consultation rather than partnership or citizen control, especially in school settings. Co-creation could be a means to support higher levels of participation, yet its definition remains unclear. A further challenge relates to the methods needed to promote participation. Examining what co-creation represents for health promoters could help in both of these respects. Objectives and goals: This study explored how school health promotion professionals perceived and defined co-creation to gain insight into how to encourage co-creation processes in school-based health promotion. Methods: Qualitative data including documents and illustrations were collected during creative thinking activities undertaken with school health promotion professionals. All data collected were transcribed and analysed using a three-stage screening process. Results: Co-creation is a multi-dimensional construct. Based on our findings, it is a voluntary-based process of bottom-up collaboration informed by values of diversity, mutual trust, openness, autonomy, freedom, respect and shared expertise, responsibility and decision-making. Co-creation can result in out-of-the-box, new or improved tailored health-promoting practices and projects, which address a co-defined need, for the benefit of all members of the group. Conclusion: Co-creation is timely and key in school health promotion practices. Further research is needed into the specific competences needed to promote co-creation, as well as the methods used to evaluate achievements and added value of co-creation at different levels of implementation.