For the past decade or so, the term "social entrepreneur" has emerged as favorite jargon in development and philanthropic circles. The term has about as many definitions and applications as it does practitioners. Generally speaking, it implies new ideas to solving social problems, approaches that are ethical and compassionate but rooted in pragmatism and real-world business practices. And, say most in the field, social entrepreneurialism must have as a goal economic growth and sustainability. If not, it's merely a charity.

Like business entrepreneurs, social entrepreneurs need capital, for both creation and expansion. As the movement in social entrepreneurialism grows, so, too, the demand for capital. As capital increases, so do opportunities. The more capital available, "the bigger the dealflow," explains Santa Clara University professor of business and ethics Kirk O. Hanson, in terminology more familiar to readers of these pages.

Mechanisms to provide that social capital have evolved and developed. Some of the money may provide seed grants, with no expectation of repayment. Others may be loans. The biggest trend in social capital over the past three years or so is what is most commonly called impact investing. Investors expect financial returns, but those monetary gains are tempered by social or environmental good. "Some value shows up in the balance sheet. Some value shows up in clean water, better education or safer neighborhoods," says Kevin Jones, who co-founded and heads the San Francisco-based organization Social Capital Markets. "It's the market side of philanthropy."

Impact investing is rapidly developing in size and scope. It "is growing like gangbusters," says Hanson, who for more than three decades has watched, studied and chronicled the development of business ethics and social responsibility, first as a longtime professor at Stanford University and more recently as executive director of the Markkula Center for Applied Ethics at nearby Santa Clara.

Some impact investing is done for a profit; some is structured as a nonprofit. Some investments are done directly, but increasingly they are channeled through private equity-like impact investment funds. There are now hundreds, says Timothy Freundlich, who heads the financial services nonprofit ImpactAssets, which also monitors other funds. Impact-Assets has identified 22 private debt and equity impact investment fund managers with more than $100 million under management, 12 of which have more than $250 million.

Social capital investors become the financial enablers of social entrepreneurialism. Here we profile some of the key players in this investment process.