Empirical studies and surveillance projects increasingly assess and address potentially adverse psychological health outcomes from the stress of military operations, but no standards yet exist for common concept definitions, variable categories, and measures. This article reports the consensus recommendations of the federal interagency Operational Stress Working Group for common data elements to be used in future operational stress research and surveillance with the goal of improving comparability across studies. Operational stress encompasses more than just combat; it occurs everywhere service members and their families live and work. Posttraumatic stress is not the only adverse mental or behavioral health outcome of importance. The Operational Stress Working Group contends that a primary goal of operational stress research and surveillance is to promote prevention of adverse mental and behavioral outcomes, especially by recognizing the preclinical and subclinical states of distress and dysfunction that portend a risk for failure of role performance or future mental disorders. Recommendations for data elements are divided into 3 tiers: core, supplemental, and emerging, including variable domains and specific measures for assessing operational stressor exposures, stress outcomes, moderating factors, and mediating processes. Attention is drawn to the emerging construct of stress injury as a generic term for subclinical operational stress, and to emerging data elements addressing biological, psychological, and spiritual mediators of risk. Methodologies are needed for identifying preclinical and subclinical states of distress or dysfunction that are markers of risk for failure of role performance and future clinical mental disorders, so that targeted prevention interventions can be developed and evaluated. Copyright © 2010 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.