To develop and validate a self-administered questionnaire to identify in people with Inflammatory arthritis (IA) Facilitators And Barriers to Physical activity (PA): the IFAB questionnaire. The development of the questionnaire included a systematic review of barriers and facilitators to PA to identify key themes, face validity assessment by 11 experts, and cognitive debriefing with 14 patients. The psychometric properties of the questionnaire were assessed by convergent validity (Spearman correlation) against the modified Health Assessment Questionnaire (mHAQ), the Fear-Avoidance Beliefs Questionnaire subscale for PA and the Tampa Scale for Kinesiophobia, internal consistency (Cronbach α) in 63 IA patients with rheumatoid arthritis (RA), axial spondyloarthritis (axSpA) or psoriatic arthritis (PsA). Reliability and feasibility were assessed in 32 IA patients. The questionnaire comprises 10 items: 4 assessing either barriers or facilitators, 3 assessing barriers, and 3 assessing facilitators. The items are related to psychological status (N = 6), social support (N = 2), disease (N = 1), environmental factors (N = 1). The validation study included 63 patients: 26 RA, 24 axSpA, 13 PsA; with mean age 52.8 (standard deviation 16.5) years, mean disease duration 12.5 (12.3) years, and 53% of women. The questionnaire was correlated (rho = 0.24) with mHAQ. Internal consistency (Cronbach α 0.69) and reliability (interclass coefficient 0.79 [95% confidence interval 0.59; 0.88]) were satisfactory, as was feasibility (missing data 12%, mean completion time < 5 min). The questionnaire allows the assessment of barriers and facilitators to PA in patients with IA. This questionnaire may guide targeted interventions to increase levels of PA in these patients.