Traditional questionnaires do not capture the complexity of how people are viewed by others and grouped into categories on the basis of what is inferred (or not) about them. This is critical in applying an intersectionality framework in research because people are negatively impacted because of "who they are" but also based on "how others see them." The purpose of this project was to develop and validate a questionnaire, grounded in intersectionality theory and a nuanced understanding of social position, that can be applied in large-scale, population-based surveys and studies. Drawing on 61 existing quantitative surveys collecting identity-based information and 197 qualitative studies on intersectionality describing the complex ways in which people's social positions are constructed and experienced, we created a draft questionnaire comprising five parts: 1) Sex and Gender, 2) Sexuality and Sexual Orientation, 3) Cultural Context, 4) Disability, Health, and Physical Characteristics, and 5) Socioeconomic Status. A draft of the questionnaire was then reviewed by experts via the Delphi process, which gauged the accessibility of the questionnaire (e.g., language used, length) and the relevance of its content using a 5-point scale and open-ended questions. These responses were ranked, analyzed, and synthesized to refine the questionnaire and, ultimately, to obtain ≥75 % consensus on each questionnaire item and response option. The SAFE questionnaire provides an opportunity to take a significant step forward in advancing our understanding of the complex, intersectional nature of social participation and marginalization.