Corporate social responsibility, stock prices, and tax policy

We model a market in which some investors get utility from owning shares of firms that engage in corporate social responsibility (CSR). In equilibrium, investors' CSR considerations influence ortfolio choices, stock prices, and CSR spending. We study tax policy designed to maximize total giving (individual and corporate) net of government tax breaks and find that its effectiveness is non-monotonic in the proportion of altruistic investors: with few or many altruistic investors, it has little impact on giving, but, at intermediate levels, effective tax policy intuitively relates the corporate tax rebate rate on giving and the cap on allowable tax savings.