Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some mid-cap stocks to your portfolio because they're big enough to have proven themselves to some degree and yet small enough to still have lots of room to grow, the Vanguard Mid-Cap Growth ETF
ETFs often sport lower expense ratios than their mutual fund cousins. The Vanguard ETF's expense ratio -- its annual fee -- is a very low 0.10%. (Vanguard is known for low fees.)
This ETF has performed reasonably, inching ahead of the S&P 500 over the past five years and beating 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.
What's in it?
More than a handful of growing mid caps had strong performances over the past year. Edwards Lifesciences
Other companies didn't do as well last year, but could see their fortunes change in the coming years. Health care information services specialist Cerner
Chipotle Mexican Grill
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.
Longtime Fool contributor Selena Maranjian, whom you can follow on Twitter, holds no position in any company mentioned. Click here to see her holdings and a short bio. The Motley Fool owns shares of Chipotle. Motley Fool newsletter services have recommended buying shares of Vertex Pharmaceuticals and Chipotle. The Motley Fool has a disclosure policy.