--- - |2+ Abstract Background Advances in international studies on self‐determination point out the need for continuous efforts to deepen its understanding and implications. The aim of this study is to obtain a comprehensive pool of items to operationalize the self‐determination construct that serves as a starting point towards a valid instrument based on the reports of others. Method We conducted a Delphi study of three rounds involving three panels of experts: ten professionals, five people with intellectual disability and six relatives of people with intellectual disability. Data analysis required both qualitative and quantitative methods. Results The initial pool of 131 items was refined through the different rounds to a final set composed of 115—some were removed and new ones were added. Content‐based evidence is provided. In this study, the present authors generated a potential valid pool of items to develop a new measurement tool based on the latest advances on the self‐determination theoretical framework. Conclusions The implications for future research focus on strengthening the knowledge of self‐determination. - Journal of Applied Research in Intellectual Disabilities, EarlyView.