Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you're looking to add diversification to your portfolio via international stocks, the Vanguard Total International Stock Index ETF (Nasdaq: VXUS) 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 thousand of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The Vanguard ETF's expense ratio -- its annual fee -- is a very low 0.18%. (Vanguard is known for low fees.) It also recently yielded 3.1%.

This ETF doesn't have much of a performance track record yet, as it's so new. But as it's a passive, low-fee index fund giving you much of the world's publicly traded stocks (with U.S.-based ones removed), its performance will simply closely track the performance of the world markets. 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 3%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
More than a handful of international companies had strong performances over the past year. U.K.-based telecom giant Vodafone (Nasdaq: VOD), up 18%, offers a 6.8% yield. It has plenty of flaws but also has a lot to recommend it, such as its 45% interest in Verizon Wireless that has generated billions in cash. It's also taking aim at the promising mobile payments market. Europe's financial woes and economic slowdown have hurt the company, though.

BP (NYSE: BP), also based in the U.K., rose about 12% and recently yielded 4.5%. It has been raising money by selling off assets, which bodes well for debt repayment, but its production has been shrinking over the past few quarters (while rivals have been upping their investment in development), leading some analysts to downgrade it. Promising, though, are its investments in wind power and biofuels, as well as its rising dividend.

Other companies didn't do as well last year, but could see their fortunes change in the coming years. France-based oil company Total (NYSE: TOT), for example, gained 7%, rebounding recently despite being plagued by troubles in Europe and falling oil prices and also operating in some unstable areas, such as Iraq. It has been expanding its operations, though, exploring in locations such as off the coast of East Africa for natural gas and investing in liquefied natural gas in Australia. It has invested significantly in renewable energies, as well. The stock recently yielded 4.8%.

Germany-based conglomerate Siemens (NYSE: SI), down 5% and also hit by Europe's turmoil, has a promising future, in part because it can help other companies cut their energy costs. The company has been investing in the growing battery business, working on batteries for cars, trams, and more. It recently announced plans to buy back up to $3.6 billion of its stock.

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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