This thesis investigates Corporate Social Responsibility (CSR), specifies its stakes, examines the communication strategies of its actors and determines the conditions of the financial impact of Environmental, Social and corporate Governance (ESG) news. The first chapter discusses the CSR theories and provides several stylized facts about its sources, its location, its lexicon and its temporal evolution. The second chapter proposes a new grid of extra-financial business rating, taking into account sectorial specificities. Thus, environment is more heavily weighted for oil companies than banks, where governance is the main issue. The third chapter analyzes the CSR communication strategies of firms, media and NGO. When criticized by external sources on one ESG concern, companies adopt a low-profile on this criterion and counter-attack by disclosing more information on the other criteria. Within a sector, firms are sheep like on their ESG major concerns; while they adopt free-riding behaviors on the minor criteria. Double-edged, firms' disclosures on major concerns have a positive effect on their public relations, but also expose them to external attacks. The final chapter examines the impact of ESG information disc10sure on the financial profitability of firms. Overall, only negative information disclosed by the media have a significant negative impact in the short run. The carrot is better reflected than the stick and the announcements of firms and NGO are not a source of abnormal returns. The firms' ESG reputation in the media is a goodwill shield against the losses following negative ESG events. Linguistic proximity and the lexicon of announces' titles also modulate their impact..
