Making money by doing good is getting easier, thanks to new legislation in four states allowing the formation of “benefit corporations,” or b-corps. Benefit corporation laws allow companies that focus on solving societal or environmental problems to make money while they’re at it. The trend is also good news for the growing ranks of individual and institutional “impact investors.”

Like other corporations, b-corps are required by law to produce shareholder value. The difference is that they are equally accountable for having a positive impact on society and the environment. Take the legislation that passed last year in Maryland, the nation’s first law allowing benefit corporations. Maryland’s law requires b-corps to provide public benefits such as “preserving the environment” and “improving human health.” All decisions made by Maryland b-corps must be weighed not just in light of shareholder or investor value, but equally in terms of “community and societal considerations” and “the local and global environment.”

Maryland’s law is a boon for “enlightened and progressive businesspeople” who are “stifled by the straitjacket requirements…of corporate law,” wrote state Senator Jamie Raskin, who sponsored the bill.

Vermont passed similar legislation in 2010, and New Jersey and Virginia have followed suit this year. Lawmakers in California, Colorado, Hawaii, Michigan, New York, North Carolina, and Pennsylvania have also introduced legislation. (California lawmakers are proposing “flexible purpose” corporations.)

A major force behind the push for b-corps is B Lab, a nonprofit near Philadelphia whose founders had a classic big, hairy, audacious goal. “We set out to create a new sector of the economy,” says Bart Houlahan, one of B Lab’s co-founders.

Houlahan went to college with the other two co-founders, Jay Coen Gilbert and Andrew Kassoy. While Kassoy went on to make hay in private equity investing, Houlahan and Gilbert built a $250 million sporting-goods business. As that company grew and fulfilled its commitment to investors, Houlahan was struck by the challenge of also fulfilling its stated commitment to employees, community, and the environment. “As we scaled up, meeting that commitment became difficult because corporations in the U.S. are set up to do one thing really well: maximize shareholder value. You can scale, but you can’t scale impact.”

The partners wanted to give socially and environmentally conscious companies and their investors a new set of rules. They formed B Lab in 2006 with a three-part plan: Create a new legally recognized corporate form, build a community of certified benefit corporations, and create an investment rating system for companies and funds.

The lawmaking piece has been driven by Bill Clark, an attorney at Drinker Biddle Reath in Philadelphia, who has written model legislation, adapts it for each state, and lobbies for the change. The new corporate form is usually met with bipartisan and almost unanimous support. “Everybody can get behind the idea of opt-in legislation that doesn’t increase the budget and doesn’t increase regulation,” notes Houlahan.

But a lot of companies don’t want to wait for legislation to make their commitment official, and that is where B Lab’s most visible work lies. It offers a free “legal roadmap” to b-corp status with suggested language to be added to a corporate charter, as well as certification. To become a “certified B corporation,” a company must achieve a baseline score on B Lab’s “impact assessment,” complete an impact assessment review with B Lab staff, and rewrite its articles of incorporation to include its social or environmental mission. If the state of incorporation also has b-corp legislation, that’s the icing on the (ethically sourced chocolate) cake.

Nearly 400 companies in 60 industries and several countries have been certified since 2007. Dansko, Method, and Numi Organic Tea are some of the more widely known brands that have taken this route.

Method, which makes environmentally safe cleaning products packaged in recycled plastic, is a “founding b corporation.” It is incorporated in Delaware, which does not yet have b-corp laws, but it revised its charter and passed B Lab’s assessment. “We amended our articles of incorporation with language stating that we will incorporate the interests of social and environmental stakeholders in our business decisionmaking,” says Method co-founder Adam Lowry. “We will certainly be one of the first to incorporate as a b-corp when the legal framework exists.”

This July, B Lab will launch the Global Impact Investment Rating System (GIIRS), a Morningstar-type rating system for socially conscious companies and funds. The goal, says Houlahan, is to “drive money to these great organizations by making their impact transparent to investors.”

To b-corps, whether they exist as such by law or by certification, transparency is essential. “Rather than just being a business that talks about the ‘triple bottom line’ of people-planet-profit, we have put it into our corporate structure so that we are required to do it,” says Method’s Adam Lowry. “We’ve made it so we are unable to violate our own business principles.”