Taking $300,000 of his own money, for example, an investor could borrow an additional $4.7 million for six months, paying 3 percent interest.

But during the long period when interest rates were falling, many investors had borrowed heavily to buy bonds.

In a buyout, investors raise and borrow funds to finance an acquisition, taking the company private.

Under such a strategy, which can be risky, an investor borrows money from a brokerage firm to buy stock.

That means an investor may borrow no more than half the purchase price.

Those investors, betting the share price will fall, borrow shares and sell them into the market.

Brokers offer margin accounts, in which investors can borrow against the value of their securities.

A short position is created when an investor borrows shares and then sells them.

In 1929, an investor could buy stock almost entirely with borrowed money; today, investors may borrow no more than half a stock's purchase price.

Any investor can lend and borrow an unlimited amount at the risk free rate of interest.