Social rating agencies (SRAs) have a dual role: on the one hand, their ratings provide information and measurement tools for the investment market, and on the other hand they incentivize firms to improve their corporate social behavior, thereby bridging the gap between society and business. SRAs use non-financial performance indicators to assess how firms deal with environmental, social and governance (ESG) issues. Their social ratings serve as a complement to traditional financial ratings for the capital markets and are also used for research on corporate social performance (CSP) in academia. Their validity and reliability has often been contested, yet little is known how SRAs actually measure social performance. This paper provides an insider’s perspective on the practices of evaluating and measuring CSP at an SRA. Our findings show that by bringing specific societal issues to the forefront of the discussion in corporate boardrooms and in the broader investment community, the agency had an impact on the firms it rated as well as on the investors. Relying on a normative approach, their proactive assessment practices opened new lines of dialogue between multiple stakeholders in society, investors and firms. A better understanding of this transformative role of SRAs helps us to develop a more dynamic account of the relationships between society and business.