The goal of the present research was to develop and test a novel conceptual model and corresponding measure of state mindfulness-the State Mindfulness Scale (SMS). We developed the SMS to reflect traditional Buddhist and contemporary psychological science models of mindfulness not similarly reflected in extant published measures of the construct. Study 1 exploratory and confirmatory factor analyses supported a higher order 2-factor solution encompassing 1 second-order state mindfulness factor, and 2 first-order factors, one reflecting state mindfulness of bodily sensations and the other state mindfulness of mental events. Study 2 provided cross-sectional evidence of the convergent, discriminant, and incremental convergent validity of SMS scores with respect to other measures of state and trait mindfulness. Study 3, a randomized control experimental mindfulness intervention study, yielded a number of key findings with respect to SMS stability as a function of time and context, construct validity, incremental sensitivity to change in state mindfulness over time, and incremental predictive criterion-related validity. Findings are discussed with respect to the potential contribution of the SMS to the study of mindfulness as a statelike mental behavior, biopsychobehavioral research on the mechanisms of mindfulness, and clinical evaluation of mindfulness. (PsycINFO Database Record (c) 2013 APA, all rights reserved).