This paper analyzes the economics of Corporate Social Responsibility (CSR), as a private response to market imperfections in order to satisfy social preferences. Depending on whether they affect regulation, competition or contracts, market imperfections driving CSR decisions are classified in three categories: public goods and bads and altruism; imperfect competition; and incomplete contracts. We successively present these drivers of CSR decisions and highlight the nature of incentives (external or internal) at work and the testable (and tested) hypotheses in the reviewed studies. We finally review the link between CSR and financial performance, as well as between CSR and social and environmental performance. A twofold discrepancy appears in the literature, opening future research paths: a disconnection between our understanding of CSR drivers and CSR impacts; and a knowledge gap between CSR financial and social consequences, the latter having received little attention.