Want to make money while helping the people around you? Impact investing may have the answer.

Funds that promise to put money to work for the good of society are growing fast, as investors look for alternatives to traditional assets.

So how does it work? Individuals invest in funds or organizations with a specific social or environmental purpose, such as building schools, hospitals or affordable housing - and they're rewarded with a financial return.

Fund managers say the unique selling point of this kind of investing is an intentional, measurable social benefit. This sets impact investing apart from its older cousins -- ethical or socially responsible investing, which try to avoid doing harm by excluding tobacco or arms companies from their portfolios.

And it appears to be catching on.

JPMorgan (JPM), which invest in several funds dedicated to social causes, says its clients weren't aware of impact investing just three years ago.

Now they're coming to the bank to pump money into socially conscious investment vehicles. A survey by the firm found investors plan to commit $9 billion this year.

World leaders are also throwing their weight behind the sector, agreeing at a G8 summit this year to create a task force aimed at expanding the market.

The global financial meltdown, financial scams and Wall Street misconduct have left many people disillusioned with traditional investments.

And growing awareness of inequality and diminishing natural resources is also fueling a hunger to do good with finance, particularly among young people.

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So what about the return on your investment?

The market is still in its infancy and tends to be weighted to private equity or longer-term funds, meaning lots of projects haven't yet had time to bear fruit.

Counting the number of jobs supported by a loan, or the amount of small businesses helped by micro-finance is straightforward.

Self-proclaimed "profit with purpose" private equity firm LeapFrog Investments says 11 million people have benefited from its investments in emerging markets.

Calculating the longer-term social impact, such as a drop in crime or reduced welfare dependency, is much harder.

Social impact bonds are designed to show more clearly how finance can generate lasting benefits.

Launched three years ago in the U.K., and now also available in the U.S., Australia and Canada, this type of bond has been used to fund school mentors, for example. It pays out if truancy rates fall.

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Getting involved is getting easier, for large and small players alike.

The Calvert Foundation offers impact investments from just $20. The group, which uses most of its capital to support projects in the U.S., has been paying returns to investors for years.

Its one-year fixed income product currently pays 0.5%. This rises to 1% over 3 years, and 3% on a 10-year term.

It won't make you rich, but beats parking money in the bank.

Investments can be made via MicroPlace, an online brokerage platform for social investing, where organizations seek backers for a variety of causes.

Calvert Foundation chief executive Jennifer Pryce says investors still need to do their homework, as fund managers are increasingly touting social investments without measurable benefit.

"They see it as a way to grow their business, by saying they do impact investing," she said.