Pain catastrophizing (PC) has been recognized as an important and consistent psychosocial predictor of nearly every key pain-related outcome. The purpose of this study was to develop a new measure of PC using modern psychometric methodology. People with chronic pain (N=795) responded to thirty items. Data were analyzed using Item Response Theory (IRT), including assessment of differential item functioning (DIF) and reliability. Sensitivity to change and validity were examined using data collected from patients undergoing spinal fusion surgery (n=184) and participating in an ongoing longitudinal aging with a disability survey study (n=1388). The final 24-item bank had no items with significant local dependence, misfit, or DIF. Results provided strong evidence of reliability and validity. Six- and 2-item short forms were developed for use when computer adaptive testing (CAT) is not feasible or desirable. The item bank was named the University of Washington Concerns About Pain (CAP) scale because the term “catastrophizing” was considered stigmatizing by people with chronic pain. Guidance for score interpretation was developed with extensive feedback from individuals with chronic pain. The CAP item bank, short forms, and user manuals are free and publicly available to all users and can be accessed online at https://uwcorr.washington.edu/measures/. PERSPECTIVE: This article presents the development of the University of Washington Concerns About Pain scale, the first IRT-based item bank of pain catastrophizing. The measure is intended for clinicians interested in improving outcomes of patients with chronic pain and for researchers who study impact of and treatment interventions aimed at reducing pain catastrophizing.Copyright © 2020. Published by Elsevier Inc.