Wider research context People with intellectual disabilities (ID) experience major health inequalities and face multiple barriers and obstacles regarding their health and health care. Like those without ID, people with ID can be mentally ill or mentally healthy. Yet, there is no common understanding or definition of positive mental health in people with ID, which impairs the validity and significance of research on this topic and ultimately limits the quality of mental health care, treatment, assessment, and mental health promotion activities. This contributes heavily to the inequalities regarding mental health in people with ID and is in direct conflict with the Convention on the Rights of Persons with Disabilities by the United Nations (UN-CRPD). Objectives The primary goal of the present project is to develop and provide the first definition of positive mental health in people with ID using a novel participatory approach. Methods A mixed methods approach in a sequential explanatory design will be applied in three steps: (1) A systematic literature review, nominal groups, and expert interviews will be used in triangulation to capture the current state of research on definitions of mental health and to explore new approaches and ideas regarding mental health for people with ID. (2) Based on the findings of the first step, a Delphi approach will be applied, including people with ID in the process. These steps will result in the first definition of mental health for people with ID. (3) Results will be disseminated to research and practice, including an impact analysis for assessing the value and significance of the project findings. Level of originality This is the first study to develop a definition of positive mental health for people with ID, thus addressing a major gap in basic research. The collected data will be used to address and establish novel aspects and concepts of mental health. We will adapt the Delphi process to assure equal inclusion of people with ID, and therefore apply an innovative, participatory research method. Furthermore, our findings will bridge the gap between science and practice. Our results will be disseminated to and evaluated with the persons concerned, i.e. persons with ID, their caregivers, and mental health professionals. Primary researchers involved The applicant for this grant is Mag. Dr. Elisabeth Zeilinger. The mentor is Univ.-Prof. Dr. Brigitte Lueger- Schuster. The co-mentor is Univ.-Prof. Dr. Luis Salvador-Carulla. Collaborators in this project are Univ.-Prof. Dr.Tanja Stamm, Univ.-Prof. Dr. Germain Weber, and Dr. Janelle Weise.