Background. Resilience influences how a person perceives and responds to pain. Both positive and negative psychosocial factors impact resilience. This is the third study in a series of Delphi studies investigating self-administered questionnaires to assess psychosocial factors in people with pain. Positive psychosocial factors (e.g., optimism, pain acceptance and social support) are considered resilience resources or mechanisms. As these factors also influence recovery from pain, management strategies to optimise these factors are being employed. Numerous self-administered questionnaires have been designed and are being used to assess these factors. This plethora of questionnaires is problematic, because in research and clinical practice different questionnaires are used to assess the same construct. This makes comparison and pooling of data difficult, especially because questionnaires that are believed to measure the same construct, often are biased toward certain aspects of the construct or also include other constructs, making the different questionnaires for a factor not interchangeable. Therefore, it is important that clinicians and researchers use uniform and the most appropriate questionnaires to assess resilience, optimism, pain acceptance and social support, to enable them to track changes during therapy and allow for pooling of data. Aims. This study aimed to identify and reach consensus on the most appropriate questionnaires to assess resilience, optimism, pain acceptance and social support in people with pain. Methods. A three-round Delphi study was conducted to achieve the aims. An international expert panel was formed consisting of 40 experts. In Round 1, experts were asked to list questionnaires that they believed were suitable to assess resilience, optimism, pain acceptance and social support in people with pain. Following Round 1, we conducted a literature review to summarise the clinimetric properties of all suggested questionnaires. In Round 2, experts received PDF-versions of all questionnaires and an overview of the clinimetric properties (internal consistency, test-retest reliability, responsiveness and construct validity) for each questionnaire. In this round, experts were asked to indicate whether they considered the questionnaires appropriate to assess that factor (Yes/No/Don’t know). At least 60% of experts had to rate the questionnaire as appropriate for the questionnaire to be retained for Round 3. In Round 3, experts rated the suitability of the questionnaires on an 11-point Likert scale (0: ‘not at all suitable’; 10: ‘completely suitable’). Consensus was considered reached if at least 75% of experts considered the questionnaire suitable (score of ≥7 on the Likert scale) and if at least 50% of experts had rated that questionnaire. Results. In Round 1, 33 questionnaires were suggested for resilience, 6 for optimism, 14 for pain acceptance and 24 for social support. Because some questionnaires were suggested for different factors, a total of 57 distinct questionnaires were suggested. Following Round 2, the number of questionnaires considered appropriate could be reduced to 8 for resilience, 2 for optimism, 6 for pain acceptance and 12 for social support. In Round 3, consensus was reached for 5 questionnaires: the Pain Resilience Scale for resilience, the Life Orientation Test (revised version) for optimism, the 8-item and revised versions of the Chronic Pain Acceptance Questionnaire for pain acceptance and the Emotional Support Item Bank of the PROMIS tool for social support. Conclusions. Via a Delphi process we have been able to make clear recommendations for the use of self-reported questionnaires to assess resilience, optimism, pain acceptance and social support in people with pain. These evidence-based recommendations will hopefully facilitate more consistent use of questionnaires to assess these factors and ultimately lead to easier comparison and pooling of clinical and research data. Limitations. A limitation of the study is that questionnaires potentially suitable to assess a factor may have been excluded from the study due to an English version not being available. Another limitation is that many experts were involved in the development, translation and/or validation of questionnaires that were included in the Delphi study which might have biased their scores. Therefore, a sensitivity analysis was performed which omitted the scores of these experts. For all questionnaires for which consensus was reached in the main analysis, consensus was also reached in the sensitivity analysis, suggesting that potential selection bias did not influence the results.