ImpactAssets, a nonprofit financial services company, introduced its annual database of fund managers who invest for maximum social, environmental and financial impact.

The managers on the ImpactAssets 50 list run $10.2 billion, which represents 15% growth over last year.

"ImpactAssets' mission is to help investors and fund managers gain access to the resources they need in order to help people double the impact of their capital, and is why we produce the annual IA 50," said Jed Emerson, ImpactAssets' Chief Impact Strategist and Chair of the ImpactAssets 50 Selection Committee.

The list includes microfinance leaders such as Accion and the Grameen Foundation USA, as well as Calvert Foundation, the not-for-profit offshoot of the pioneering SRI investment company. But the list is not limited to boutiques and specialist firms. Mainstream firms who've cracked the list include Bank of America/Merrill Lynch Capital Access Funds Management.

ImpactAssets stresses that the IA 50 is not an investable index, nor a ranking by performance or assets, but an attempt to show first-time investors the breadth and depth of firms working in the field. So new entrants have not necessarily just crossed a threshold of assets or hit a performance target to make the list.

"As we look at the space as a whole, it's a landscape overview, so if there are new funds that represent a geography or industry not represented, want to add that," Emerson said. "We're trying to show breadth of the field and depth of work in the field, so as the landscape changes, we'll reflect that."

The firms on the list and a few hundred others have been gathering capital and creating investment funds for several years so investors can more easily pick an area they want to invest in. That could be geographic, such as Africa or Asia, or thematic, such as microfinance, education or health care. "This is a starting place for financial advisors and clients to have that conversation about impact investing and whether it's a good fit for them," Emerson said.

Because the list doesn't want to stress size, it gives only broad categories of assets under management - more than $100 million, $51 million - $100 million and so on. But the biggest of the big are: BAML Capital Access Funds Management, Craft3, Lyme Timber Company, Small Enterprise Assistance Funds and Travois Holdings.

If the concept of impact investing sounds familiar, it is.

The impact investing movement is a close relative to socially responsible investing. SRI generally starts with avoiding certain industries such as guns or tobacco, and then supports companies with positive or sustainable practices in the arenas of environment and human rights. SRI, as practiced by large institutional investors such as Calpers, can also attempt to change the policies of companies it considers to have a poor record in those areas by taking large ownership stakes. SRI managers have long asserted that by investing in companies with superior records in respecting the environment and human rights, they are buying best-of-breed companies that are more innovative and incur less risk than their less scrupulous competitors.       

Impact investing differentiates itself by drawing a more direct line between the actual dollars an investor has put in and the impact the investment has had on a community. In that sense, it is very similar to microfinance. And although impact investors could choose to receive below-market returns, the aim is to receive competitive financial returns as well as make a positive social and environmental impact.

Another key difference is impact investing also tends to invest more in private equity and debt, which proponents say allows for greater transparency. (SRI practitioners can theoretically invest in any asset class, but the majority of large SRI mutual funds most investors are familiar with stick to stocks.) Impact investors also say it easier to measure the performance of their investment in terms of social and environmental impact.

"Because of the nature of private equity and debt investing versus public equity investing, you're looking at smaller businesses," said Emerson. "Some of these investors are actually on the boards of directors, so they're closer to the actual business development and execution process than if they were invested in Wal-Mart or a larger transnational."

The firms on the list and a few hundred others have been gathering capital and creating investment funds for several years so investors can more easily pick an area they want to invest in. That could be geographic, such as Africa or Asia, or thematic, such as microfinance, education or health care. Emerson stressed that the IA 50 is not an investable index, but an attempt to show first-time investors the breadth and depth of firms working in the field. "This is a starting place for financial advisors and clients to have that conversation about impact investing and whether it's a good fit for them," Emerson said.

The companies on the list must have at least $5 million in assets under management and at least three years of impact investing under their belts.