Offer your thoughts or opinion on the input financial query or topic using your financial background.

If I sell a stock that I don't have, am I required to buy it before a certain amount of time?
Answers here are correct but I'll offer an extremely (overly) simple explanation that should help you in understanding the more detailed answers.  When most people own stock they do so through a broker.  Unless you jump through some hoops, the broker keeps the shares in the name of the brokerage.  This is called holding the stock in street name. When you sell short through a brokerage, the broker is letting you borrow a certain number of shares owned by someone else and sell them for cash now.  At some point, you need to repay this loan with the same number of shares you borrowed.  Ideally, you want the stock to drop to $0.  The reason you might be forced to purchase the stock is that the actual owner(s) of the stock want to sell.  If the broker has too many people wanting to sell, you will need to repay some of all of the loan (in shares) i.e. purchasing shares at the current market price.