Diversification is not an end in itself, but rather a way to mitigate portfolio risk. So the question of "How many stocks should I own?" will be different for everyone … but still, there are some good principles to think about.

Eddy Elfenbein, who writes about investing at Crossing Wall Street, is known for being a buy-and-hold investor -- CNNMoney named him "the best buy-and-hold blogger" on the Web -- and on his site, he has a public portfolio of 20 stocks. Last month, during an hourlong interview in Washington, D.C., I asked him whether he thought 20 stocks made for a diversified portfolio. Watch the following video for our exchange. (Run time: 1:40; a transcript follows the video.)

Fool.com managing editor Brian Richards holds no position in any company mentioned. The Motley Fool owns shares of Oracle, Apple, and Google. Motley Fool newsletter services have recommended buying shares of Google and Apple. Motley Fool newsletter services have recommended creating a bull call spread position in Apple. We tell you all this because of the Fool's disclosure policy.