This dissertation examines three research questions on institutional investing and corporate responsibility. First, I focus on institutional investors with a high commitment to responsible investing and examine their influence on environmental and social firm performance. I find that these investors alone drive the positive link between institutional ownership and corporate sustainability. The same investors also play a critical role in the success of collaborative engagements and in preventing adverse corporate incidents. The results advocate a differentiated view on institutional investment and corporate sustainability. Second, I examine if ownership by passive investors influences firms toward more long-term-oriented action, using an international sample of more than 28,000 companies. Firms with high passive ownership invest more in R&D, file more patents, strengthen their organizational capital, and use more long-term-oriented language in their annual disclosure. My findings suggest that passive ownership has the potential to curb shorttermism at the level of the firm. Third, I study the effect of equity index membership on environmental firm performance based on a unique international dataset of 132 index launches. I find that firms added to new stock indexes significantly alter environmental sustainability. The same companies also amend their CSR-related disclosure while increasing accounting profitability. The results suggest that stock indexes constitute a salient mechanism influencing the norms of corporate behavior.weiterlesen