Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect the global infrastructure industry to take off as the world's economies heat up and demand grows for improvement projects, energy, and more, the iShares S&P Global Infrastructure Index ETF (NYSE: IGF) 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 lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The iShares ETF's expense ratio -- its annual fee -- is a relatively low 0.48%. It was recently yielding a solid 4.5%, as well.

This ETF outperformed the world market over the past year, but underperformed it over the past three. 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 16%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
Plenty of global infrastructure companies had strong performances over the past year. Duke Energy (NYSE: DUK) surged 23%, partly on optimism over its merger with Progress Energy as well as its growing investments in renewable energy production. It has run into a bit of trouble with the North Carolina Utilities Commission, though, which is looking into why it dismissed Progress CEO Bill Johnson right after the merger.

Natural gas specialist Spectra Energy (NYSE: SE) gained 15%. Its revenue growth rate has been increasing in recent years, and it recently opened a new natural gas processing plant in British Columbia. It's also expanding its pipeline to deliver more natural gas capacity to the New York-New Jersey region.

Other companies didn't do as well last year, but could see their fortunes change in the coming years. Exelon (NYSE: EXC), down 6%, is the nation's largest nuclear plant operator, and has suffered some as nuclear power lost a bit of its luster after the Fukushima disaster. Recently yielding 3.9%, much of its future depends on how the cost of producing nuclear power compares with other alternatives, such as natural gas. Right now, nuclear power is relatively expensive to produce.

Down 5%, India-based Tata Communications (NYSE: TCL) recently completed the first round-the-world fiber-optic network, and boasts the world's largest sub-sea cable network, as well. Many at Fool HQ are not big fans of high-frequency trading, but Tata is facilitating that via a "low-latency" network linking markets in Asia with Europe and the U.S.

The big picture
A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

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