In this edition of The Motley Fool's "Ask a Fool" series, Motley Fool analysts Jason Moser and Brendan Mathews take a question from a reader who asks, "How many companies should I own?"

Brendan starts by suggesting that investors own at least 15 companies. That will allow at least a minimum amount of diversification. Beyond that, it really depends on the investor's situation and preferences. Some investors like to own a lot of stocks to increase their diversification. Others like to focus on their best ideas. That's how Jason likes to invest, and he describes why.