Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect the world's developing economies to keep developing, and at a faster clip than our developed economy, the Vanguard MSCI Emerging Markets ETF (NYSE: VWO) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in several dozen of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The emerging markets ETF's expense ratio -- its annual fee -- is a very low 0.22%.

This ETF has performed rather well, outperforming broader international benchmarks handily over the past three and five years. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

With a low turnover rate of 12%, 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. Sasol (NYSE: SSL), the world's top maker of motor fuels from coal and gas, gained about 42% over the past year. It's expanding its presence in Canada through a deal with Talisman Energy (NYSE: TLM), and is looking good with solid growth and a healthy balance sheet. Brazilian miner Vale (Nasdaq: VALE) gained about 34%. While some see it as a still-inexpensive fast-grower, profiting along with fellow iron-ore giants Rio Tinto (NYSE: RIO), and BHP Billiton (NYSE: BHP) from iron-ore prices and strong demand for steel, others are cautious about the company now, as it has a new CEO. 

Other companies didn't add as much to the ETF's returns last year but could have an effect in the years to come. Brazilian oil company Petrobras (NYSE: PBR) slid by around 6%, but it's sitting on massive reserves and is developing offshore fields.

The big picture
Emerging markets are likely to keep emerging for a long time. 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 holds no position in any company mentioned.  Check out her holdings and a short bio. The Motley Fool owns shares of Vanguard MSCI Emerging Markets ETF and Petrobras. Motley Fool newsletter services have recommended buying shares of Petrobras and Sasol. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.