Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some emerging-market stocks to your portfolio but don't have the time or expertise to hand-pick a few, the SPDR S&P BRIC 40 (NYSEMKT: BIK) ETF could save you a lot of trouble. Instead of trying to figure out which emerging-market stocks will perform best, you can use this ETF to invest in lots of them simultaneously. It holds stock in about 40 major companies based in Brazil, Russia, India, and China (the "BRIC" countries).

The basics
ETFs often sport lower expense ratios than their mutual-fund cousins. This ETF, focused on emerging-market stocks, sports a relatively low expense ratio -- an annual fee -- of 0.5%. The fund is fairly small, too, so if you're thinking of buying, beware of possibly large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This emerging-market stocks ETF has outperformed the MSCI EAFE index over the past five years and lagged 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.

Why emerging-market stocks?
Emerging markets rightfully draw the attention of many investors because they can offer greater growth rates as their economies develop.

More than a handful of emerging-market stocks had strong performances over the past year. Search engine giant Baidu (BIDU -0.61%) gained 36%, for example, growing its business briskly. As my colleague Matthew Frankel has noted, Internet usage is growing rapidly in China, and Baidu's "revenues have more than quintupled in the past five years, and are expected to increase by another 39% this year and 33% next year." Bulls like Baidu's profitability and growth prospects, such as in video, smart TVs, and mobile apps. Analysts at Citi estimate that about a third of Baidu's search traffic comes from mobile users. Also promising is its "Light App" strategy that could profit from sales of less popular apps, capturing the "long tail" of the market.

Other emerging-market stocks didn't do quite so well over the last year but could see their fortunes change in years to come. Brazil-based Vale (VALE 0.56%), the world's largest iron-ore concern (though Rio Tinto is about to take that title away), shed 3%. Focusing on its most promising opportunities, such as iron, Vale has been cutting costs aggressively and selling assets. It's looking to shed its stake in aluminum producer Norsk Hydro and bauxite producer Mineracao Rio do Norte. Demand from China seems to be growing, which bodes well for Vale. Patient believers can collect a dividend while they wait for this cyclical company to enjoy brighter days, but its payout has been uneven.

China Life Insurance (LFC) dropped 12%. In its first quarter, it reported operating earnings up 79%, leading to an analyst upgrade to "outperform" from Zacks. However, Zacks has just downgraded the stock to "neutral," seeing China Life facing more intense domestic competition and "waning" cash-flow levels. On the plus side, the company's foray into private equity holds great potential. The company is one of the world's largest life-insurers, but it doesn't seem to be near bargain levels lately. Our analysts didn't rank it near the top of a five-company group.

Brazil's Petrobras (PBR 1.41%) fell 28%. It has been burdened by significant debt and has had to deal with government interference in its business as well. The government, for example, has kept gas prices below Petrosbras' costs. Bulls have been heartened by rising production numbers as a few offshore rigs are brought back into service, and some are hopeful that solid car sales in Brazil will boost Petrobras' business, too. Petrobras has a $237 billion investment program underway and expects to double its production in coming years. It's the biggest participant in a consortium that will engage in ultra-deepwater drilling off Brazil's coast.

The Big Picture
Consider adding emerging-market stocks to your portfolio. 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.