We study a firm’s decisions to engage in socially responsible activities, voluntarily report on them, and purchase external assurance of the report. In our signaling model, neither firm type nor the level of activity is observed. We show that if voluntary assurance is not too expensive, the firm that engages in more socially responsible activities purchases external assurance and thus “selects” a separating equilibrium. As a result, CSR reports can be used to infer the level of activity and this causes all firms to engage in more socially responsible activity. Further, when voluntary assurance is required to support a separating equilibrium, greater monitoring by social activists increases the chosen quality of voluntary assurance—voluntary assurance and monitoring by social activists are complements, not substitutes.