Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect to see big global investments in infrastructure, particularly in emerging markets, in the coming years, the PowerShares Emerging Markets Infrastructure ETF (NYSE: PXR) 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 all at once.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The PowerShares ETF's expense ratio -- its annual fee -- is on the steep side for an ETF, at 0.75%, but that's still lower than the average actively traded mutual fund.

This ETF has performed well, but it's also very young, with just two years on the books. It jumped about 90% in 2009, and beat the market in 2010. As with most investments, we can't expect outstanding performances in every quarter or year -- what matters is the long haul, and the future. Investors with conviction need to wait for their holdings to deliver.

With a relatively low turnover rate of 36%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do. That'll give its holdings a better chance to perform.

What's in it?
The fund is nicely balanced between large-caps and mid-caps, and holds about 90% of its assets in industrial materials, as you'd expect from an infrastructure-focused ETF. Several of this ETF's components made strong contributions to its performance over the past year. Caterpillar (NYSE: CAT) has been on fire lately, gaining 87% over the past year as it expands the scope of its capabilities. Many investors are excited about its purchase of surface-mining equipment specialist Bucyrus (Nasdaq: BUCY), which itself recently bought the mining-equipment assets of Terex (NYSE: TEX).

Switzerland-based ABB (NYSE: ABB) gained 35% over the past year delivering power technologies for utility and industrial customers. My colleague Eric Bleeker also considers it a sneaky alternative-energy play, since its wares can help transport cleaner energy to locations that need it. Foster Wheeler (Nasdaq: FWLT), meanwhile, is involved in creating more power plants and refineries, and has gained about 30% over the past year.

The PowerShares ETF isn't the only ETF that focuses on global infrastructure growth. But its balance over many nations and companies makes it particularly intriguing these days.

The big picture
A well-chosen ETF can grant you instant diversification across an 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 ."

We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.

Longtime Fool contributor Selena Maranjian does not own shares of any companies mentioned in this article. ABB is a Motley Fool Global Gains pick. Try any of our investing newsletter services free for 30 days. The Motley Fool is Fools writing for Fools.