Laurence “Larry” Fink, the founder and CEO of BlackRock, the world’s largest asset manager, which has more than $6 trillion in assets under management, issued an open letter to CEOs this past January—and reportedly sent many of them into a tizzy. Fink’s letter said society is demanding that companies, public and private, need to “serve a social purpose,” benefiting not just shareholders but also employees, customers, and neighbors. And, he explained, from that point forward, BlackRock would be “eager to participate in discussions about long-term value creation and work to build a better framework for serving all your stakeholders.” Executives, he wrote, should be able to answer their questions about the company’s actions. For example, what role does the company play in the community? How is it managing its impact on the environment? Is it working to create a diverse workforce? “The time has come for a new model of shareholder engagement,” he wrote.

For nearly 50 years, many have been guided by the idea, laid out most famously by Milton Friedman, that the most appropriate way to create social change is to give profits to investors, and taxes to the government, and use that money to make an impact. For just as long, other investors have argued in favor of divesting from companies to make a political or social point—dumping shares of gun manufacturers or fossil fuel companies, for example.

But with the rise of index funds, divesting from individual company stocks has become more difficult, even though there are some funds that try to do this by designing a basket that tracks an index while excluding “sinful” stocks. It can even be counterproductive.

Investing with a social motivation has moved from divesting from certain companies based on values or preferences to a more regular form of seeking alpha, by investors who hope their stakes will generate returns as well as save the world. Like financial philanthropists trying to affect specific social issues, these investors are often using markets and investing tools to shift behavior and create change. As a result, there are big shifts in thinking about the role of investors, who have had the luxury of worrying primarily about profits. Some prominent managers and investors are advocating for joining other stakeholders to push for change. “I certainly view the letter as symbolic that this is becoming more mainstream,” says Chicago Booth’s Robert H. Gertner, who this spring discussed Fink’s letter on a panel with BlackRock cofounder Sue Wagner.

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