PROJECT SUMMARY/ABSTRACT Mindfulness interventions are efficacious treatment options for individuals struggling with a wide range of psychiatric disorders and stressors. Though the use of mindfulness interventions has grown, mindfulness research relies primarily on self-report measurement as treatment targets. As such, the field currently lacks a reliable and valid implicit measure of non-judgment of internal experiences as it relates to mindfulness. Experts in the research field have recently expressed an urgent need for expanded target measures of mindfulness interventions, and this project proposes to answer this call by adapting a validated implicit measure (Word Sentence Association Paradigm; WSAP) to examine non-judgment of internal experiences (WSAP-NJ). In following the rigorous model for measure development set forth by the PROMIS group, the first step of this project will be to conduct a systematic literature review of the current available implicit, performance-based, and behavioral measures of mindfulness. The research team will draw on experts within the mindfulness research field to develop an operational definition of non-judgement of internal experiences, and develop a pool of 100 items to be used in the WSAP-NJ. To complete a pilot test of the WSAP-NJ, we will draw from participants already enrolled and completing the Sponsor’s and Co-Sponsor’s ongoing funded research studies through the Mindfulness Center at Brown University and Butler Hospital. One hundred participants will complete the WSAP-NJ, and analyses will be run to examine the internal consistency, reliability, and factor structure of the WSAP-NJ, as well as examine its convergent and divergent validity. Furthermore, we will have the ability to examine the sensitivity to change of the WSAP-NJ by administering the WSAP-NJ to participants of a study examining an app-based mindfulness treatment program for anxiety at multiple time points (baseline, 1-month follow up, and 2-month follow up). This pilot study of the WSAP-NJ will provide preliminary data to inform further field testing of the measure.