Want to invest in “high-quality, attractively priced companies making a positive impact on the world”? Of course you do.

The question is, will you make money?

On Sept. 30, Thornburg Investment Management launched the Better World International Fund, self-described above. But if you have less than $2.5 million to invest, the fund will charge you an upfront "load" of up to 4.5 percent and an annual expense ratio of 1.83 percent. A no-load alternative version of the fund charges 2.38 percent of assets a year.

That’s just about how much non-U.S. stocks have earned annually over the past 20 years and 11 times as much as the fees on the most popular U.S. international mutual fund.

The new fund’s portfolio manager, Rolf Kelly, said investors will get something for the higher fees. “There is an additional layer of work and effort that’s going into this product,” he said, citing the costs of evaluating companies in emerging markets. “It’s up to us to prove our salt and earn our fees. It’s my job to justify my existence.”

Investors can expect to hear more and more sales pitches such as this one. Mainstream investment firms are rushing into “sustainable investing,” also known as SRI (socially responsible investing) and ESG (environment, social, and corporate governance). From 2012 to 2014, the number of U.S. investment funds incorporating ESG criteria jumped 28 percent, to 925, and their assets more than quadrupled, to $4.3 trillion, according to the Forum for Sustainable & Responsible Investment. Even the largest Wall Street firms are getting into the act. BlackRock, the biggest money manager in the world, started selling its BlackRock Impact U.S. Equity Fund on Oct. 13.

“The driver is client demand,” said Kathy Leonard, a 32-year veteran of sustainable investing who is a wealth advisor at UBS Financial Services in Boulder, Colo. “We need to have the products and services that our clients are asking for.”

Expect that demand to spike after an Oct. 22 ruling from the U.S. Department of Labor's Employee Benefits Security Administration. The ruling makes it clear that managers of pensions and 401(k)s should feel free to add ESG funds to their lineups. Previously, many avoided sustainable options for fear of violating complicated federal regulations governing retirement plans.

It’s never been easier to find an investment that promises to do good. It’s never been harder to sort through the jargon and marketing pitches to find a sustainable strategy that’s right for you.

Five Don'ts: Don’t Overpay

No matter how well-intended an investment strategy may be, it can’t avoid mathematical reality: Every dollar investors pay in fees subtracts from returns. But there are cheaper sustainable options, including index funds. The Calvert U.S. Large Cap Core Responsible Index Fund charges an expense ratio of 0.19 percent. The Vanguard FTSE Social Index Fund charges 0.27 percent.

Investors may decide to pay more, and not only because they think they’ve found the rare portfolio manager who can outperform the indexes. For example, they may want a manager who takes the time to sponsor shareholder resolutions that push companies to behave more ethically or responsibly, by one definition or another. That kind of activism might not always pay off financially, but that’s not necessarily the point.

Still, investors shouldn’t have to sacrifice their returns altogether for their values. “Companies are going to charge what they can get away with,” said Sonia Kowal, president of Zevin Asset Management. In general, an actively managed SRI or ESG fund shouldn’t cost more than a typical non-ESG actively managed fund, she said. According to the Investment Company Institute, the average investor pays an annual expense ratio of 0.86 percent for actively managed stock funds. And the more you have to invest, the less you should pay.

Don’t Expect Huge Returns

A common pitch is that sustainable investments perform better than other assets. The idea is that ethical and responsible companies are less risky and better long-term investments.

It might even be true. In a March 2015 analysis by the University of Oxford and Arabesque Asset Management, 80 percent of academic studies found that the stocks of companies with “good sustainability practices” do better than other stocks.

But it can cost money to find these companies, in the form of fees that detract from returns. And even the best-paid, most-experienced analysts can make mistakes. Until Oct. 6, Volkswagen was included in the Dow Jones Sustainability Indices.

Sustainable strategies’ real-world track record is mixed. Morningstar estimates that social impact funds returned about 5 percent a year over the past 10 years, lagging behind large-cap funds by 1.1 percentage points a year. When you look at index funds, it’s hard to distinguish the performance of socially responsible funds from that of their non-SRI peers. The Vanguard FTSE Social Index Fund has beaten Vanguard’s S&P 500 fund over the past five years but lagged over the past decade.

Don’t Let The Jargon Throw You

Terms such as sustainable, impact, ESG, and SRI can all mean different things to different people. “We’ve got a terminology problem,” said Leonard of UBS.

Take the “ESG integration.” More and more fund managers are pledging to integrate ESG factors into their investment process. For many of those managers, however, ESG remains just one factor of many. They might still end up owning the tobacco, fossil fuel, or defense stocks you thought you were avoiding.

Even based on the same values, there's a ton of ways to invest. Some investors will want to exclude companies with questionable practices; others end up owning those companies and pushing executives to do better. Some just try to buy the best- behaving companies in each industry, so they are fully diversified; others double down on industries they want to encourage—for example, by buying solar stock funds.

The CFA Institute, a nonprofit group for investment professionals, has a free online course that can help you sort through the many approaches to ESG investing.

Don’t Dither

With so many choices, investors need to know their top priority, and “doing good” isn’t specific enough. “What is it you feel strongly about?” said Usman Hayat of the CFA Institute.

You might decide your first goal is avoiding stocks that violate your religion or your social values. No alcohol or no gun stocks, for example. If you decide your top priority is making money, you may go for a more flexible approach.

Don’t Expect Perfection

Of a stock, a fund, or yourself.

No company does only good in the world. A solar company might not treat its workers well, for example. A gay-friendly company might be a big polluter. “Investors need to realize that there is no perfect solution out there,” Hayat said.

And while a sustainable investing strategy may make the world a better place, even the most virtuous investors inevitably make compromises.