The issue of how an activist identity develops is one of the core issues in social psychology and social movement research. Because of problems in the measurement of individuals' propensities to engage in social action, however, findings in this area are often equivocal, and cross-study comparisons and conclusions are difficult to draw. Hence, the aim of these studies was to develop a measure to assess individuals' propensities to engage in social action. This measure, the Activism Orientation Scale (AOS), demonstrates strong psychometric properties and allows assessment of activist propensity across a wide continuum of social action behaviors, ideological positions, and movement issues. Additionally, the broad applicability of the A OS allows for its use by researchers, activists, and policymakers.