Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you want to invest broadly and in a socially responsible fashion, the iShares MSCI USA ESG Select Social ETF (NYSE: KLD) could save you a lot of trouble.

You can use this ETF to invest in gobs of ethical, sustainable contenders simultaneously. It tracks the MSCI USA ESG Select Index, which seeks companies that outrank their peers on environmental, social, and governance (ESG) counts.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. This ETF's expense ratio -- its annual fee -- is 0.50%. That's relatively low compared to mutual funds, but fairly high for a broad-market index ETF.

The ETF has performed reasonably, outperforming the S&P 500 over the past three and five years by a small margin. As with most investments, of course, we can't expect outstanding performances in every quarter or year, but it's likely that this ETF's returns won't stray too far from the S&P 500's, as there's quite a bit of overlap. Investors with conviction need to wait for their holdings to deliver. With a relatively low turnover rate of 35%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
Several of this ETF's components made strong contributions to its performance over the past year. Johnson Controls (NYSE: JCI) gained about 48% over the past year as it pursues solid environmental goals, such as cutting its ratio of energy use to revenue by 30%, its waste by 20%, and its water use by 10% by 2018. Oracle (Nasdaq: ORCL) gained about 43%, reducing its energy usage and delivering software solutions to companies that include the ability to track and report their greenhouse emissions.

Other companies didn't add quite as much to the ETF's returns last year, but could have an effect in the years to come. Intel (Nasdaq: INTC), for instance, gained 15% developing more efficient 3-D chip technologies and pleasing shareholders with dividend increases and share buybacks.

Aflac (NYSE: AFL), meanwhile, has lost 4% of its share value over the past year, partly due to most of its business being based in disaster-ridden Japan. But while other insurers in the area, such as MetLife (NYSE: MET), face property damage claims, Aflac specializes mostly in supplemental health insurance, so it should fare better.

The big picture
A well-chosen ETF can grant you instant diversification across the industry -- and make investing in and profiting from the sector that much easier.

ETFs can help you find the way to better investing results. To find some great ETF investing ideas, take a look at The Motley Fool's special free report, "3 ETFs Set to Soar During the Recovery."

Longtime Fool contributor Selena Maranjian owns shares of Intel, but she holds no other position in any company mentioned. Click here to see her holdings and a short bio. The Motley Fool owns shares of Oracle, Aflac, and Intel, and has bought calls on Intel. Motley Fool newsletter services have recommended buying shares of Aflac and Intel, as well as creating a diagonal call position in Intel. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.