question about short selling stocks
If you had an agreement with your friend such that you could bring back a substantially similar car, you could sell the car and return a different one to him.  The nature of shares of stock is that, within the specified class, they are the same.  It's a fungible commodity like one pound of sand or a dollar bill.  The owner doesn't care which share is returned as long as a share is returned.   I'm sure there's a paragraph in your brokerage account terms of service eluding to the possibility of your shares being included in short sale transactions. The original owner of the shares can pledge their shares to be short, and they earn interest from lending their shares. The conditions of this arrangement are detailed in standard agreements all market participants sign with their broker, or clearinghouse, or with the exchange, or with the self regulatory agency. Stocks within the same class are identical, despite someone's sentiment to an old share certificate that their grandparents gave them, and as such can be sold and returned to the beneficial owner multiple times with no difference. That is how it is supposed to work anyway, as naked shorting involves selling fictional shares that have no beneficial owner. So there are market inefficiencies in this practice, but the agreements between market participants are sound and answers your question about how. "My take on this is that with any short-selling contract you are engaging in, at a specified time in the future you will need to transfer ownership of the item(s) you sold to the buyer. Whether you own the item(s) or in your case you will buy your friend's used  car in the meantime (or dig enough gold out of the ground - in the case of hedging a commodity exposure) is a matter of ""trust"". Hence there is normally some form of margin or credit-line involved to cover for you failing to deliver on expiry."
How so? If i sell short, then i make a profit only if the price goes down so i can buy back at a lower price. Yes, but if the price is going up then you would go long instead. Shorting a stock (or any other asset) allows you to profit when the price is going down. Going long allows you to profit when the price is going up. In the opposite cases, you lose money. In order to make a profit in either of those situations, you have to accurately assess which way the price will trade over the period of time you are dealing with. If you make the wrong judgment, then you lose money because you'll either sell for a lower price than you bought (if you went long), or have to buy back at a higher price than you sold for (if you went short). In either case, unless the trader can live with making a short-term loss and recouperating it later, one needs a good stop-loss strategy. I agree with Mark.  I was quite confuse about the short position at first but then I did a lot of learning and found out that as long as you have enough cash to cover your margin requirement you do not pay any interest since you do not have a debit on your margin balance.  This is not true for a long position though, supposed you have 5k cash and 5k margin balance, if you buy 10K worth of stocks then you will need to pay interest on the 5k of the margin balance since it is a debit.  Since shorting is done at a credit basis, you actually get interest from the transaction but you still may need to pay the borrowing fees for the stocks so they could simply balance each other out.  I have shorted stocks twice through two different companies and neither time I noticed any interest charges.  But make sure you have enough cash to cover your margin requirement, because once your margin balance is used to covered your position then interest would accrual. Learn. For every seller, there's a buyer. Buyers may have any reason for wanting to buy (bargain shopping, foolish belief in a crazy business, etc).  The party (brokerage, market maker, individual) owning the stock at the time the company goes out of business is the loser . But in a general panic, not every company is going to go out of business. So the party owning those stocks can expect to recover some, or all, of the value at some point in the future. Brokerages all reserve the right to limit margin trading (required for short selling), and during a panic would likely not allow you to short a stock they feel is a high risk for them. "The question you are asking concerns the exercise of a short option position.  The other replies do not appear to address this situation. Suppose that Apple is trading at $96 and you sell a put option with a strike price of $95 for some future delivery date - say August 2016.  The option contract is for 100 shares and you sell the contract for a premium of $3.20. When you sell the option your account will be credited with the premium and debited with the broker commission.  The premium you receive will be $320 = 100 x $3.20.  The commission you pay will depend on you broker. Now suppose that the price of Apple drops to $90 and your option is exercised, either on expiry or prior to expiry.  Then you would be obliged to take delivery of 100 Apple shares at the contracted option strike price of $95 costing you $9,500 plus broker commission.  If you immediately sell the Apple shares you have purchased under your contract obligations, then assuming you sell the shares at the current market price of $90 you would realise a loss of $500 ( = 100x($95-$90) )plus commission.  Since you received a premium of $320 when you sold the put option, your net loss would be $500-$320 = $180 plus any commissions paid to your broker. Now let's look at the case of selling a call option.  Again assume that the price of Apple is $96 and you sell a call option for 100 shares with a strike price of $97 for a premium of $3.60.  The premium you receive would be $360 = 100 x $3.60.  You would also be debited for commission by your broker. Now suppose that the price of Apple shares rises to $101 and your option is exercised.  Then you would be obliged to deliver 100 Apple shares to the party exercising the option at the contracted strike price of $97.  If you did not own the shares to effect delivery, then you would need to purchase those shares in the market at the current market price of $101, and then sell them to the party exercising the option at the strike price of $97.  This would realise an immediate loss of $400 = 100 x ($101-$97) plus any  commission payable.  If you did own the shares, then you would simply deliver them and possibly pay some commission or a delivery fee to your broker.  Since you received $360 when you sold the option, your net loss would be $40 = $400-$360 plus any commission and fees payable to the broker. It is important to understand that in addition to these accounting items, short option positions carry with them a ""margin"" requirement.  You will need to maintain a margin deposit to show ""good faith"" so long as the short option position is open.  If the option you have sold moves against you, then you will be called upon to put up extra margin to cover any potential losses." If you buy puts, there are no guaranteed proceeds though.  If you short against the box, you've got immediate proceeds with a nice capital loss if it doesn't work out.  Conversely, you could write a covered call, take the contract proceeds, and write off the long position losses.  Nobody ever factors tax consequences into the equation here. Shorting Stocks: Borrowing the shares to sell now. Then buying them back when the price drops.  Risk: If you are wrong the stock can go up. And if there are a lot of people shorting the stock you can get stuck in a short squeeze.  That means that so many people need to buy the stock to return the ones they borrowed that the price goes up even further and faster.  Also whoever you borrowed the stock from will often make the decision to sell for you. Put options. Risk: Put values don't always drop when the underlying price of the stock drops. This is because when the stock drops volatility goes up. And volatility can raise the value of an option. And you need to check each stock for whether or not these options are available. finviz lists whether a stock is optional & shortable or not. And for shorting you also need to find a broker that owns shares that they are willing to lend out. Yes, just set aside the amount of money. If you buy a cfd long in a stock for a 1000$, set aside 1000$. If you buy a cfd short, set aside the same amount and include a stoploss at the value at which the money is depleted. In this case however, you can stil lose more, because of opening gaps. By doing this, you replicate the stock return, apart from the charged interest rate. The answer provide by @mbhunter is correct, however there are contexts, shorting in spot market and carrying the position over settlement usually does not entail payment of dividend to the broker, one of the reason being post ex-date the price of the share downward adjusts to the extent of the dividend, so practically if you have shorted at 100 and post ex-date (assuming a dividend of 2 and no movement of the stock price), the price would slide to 98, the party who longed the stock @ 100 now is sitting on a price of 98 and received a dividend of 2 which equates to 100. The above is also contextual to the law of the country governing the exchange and the security exchange board regulations. Adding to the answers above, there is another source of risk: if one of the companies you are short receives a bid to be purchased by another company, the price will most probably rocket... "If you sell a stock you don't own, it's called a short sale. You borrowed the shares from an owner of the stock and eventually would buy to close. On most normal shares, you can hold a short position indefinitely, but there are some shares that have a combination of either a small float or too high a short position that shares to short are not available.  This can create a ""short squeeze"" where shorts are burned by being forced to buy the stock back.  Last - when you did this, you should have instructed the broker that you were ""selling to open"" or ""selling short."" In the old days, when people held stock certificates, you were required to send the certificate in when you sold. Today, the broker should know that wasn't your intention." Your question has 6 questions marks along with comments on what you'd like to know.  Yes, there are stocks that are tough to short, a combination of low float, high current short positions, etc. Interest charged on the position rises in a supply/demand fashion.  To unwind the position, there's always going to be stock available to buy. A shortage of willing sellers will cause the price to go up, but you'll see a bid/ask and the market will clear, i.e. The buy order fills. Short sellers have to pay interest on the borrowings to the shareholders. Although many times brokers don't pass on these earnings to the shareholders, this is the exchange. The problem with short options is they expire and have to be covered. An inverse ETF is the way to go in my opinion. Because the real issue isn't if the market is overvalued but when will it correct. That's the risk and no one knows that answer why can't I just use the same trick with my own shares to make money on the way    down? Because if you sell shares out of your own portfolio, by definition, you are not selling short at all. If you sell something you own (and deliver it) - then there is no short involved. A short is defined as a net negative position - i.e. you sell shares you do not have. Selling shares you own is selling shares you own - no short involved. You must borrow the shares for a short because in the stock market, you must DELIVER. You can not deliver shares you do not own. The stock market does not work on promises - the person who bought the shares expects ownership of them with all rights that gives them. So you borrow them to deliver them, then return them when you buy them back. It's extremely divisible. The smallest unit is 0.00000001 BTC. This smallest unit is called a satoshi, after the pseudonym of the inventor of Bitcoin.  I suggested to my friends and family back in mid 2015 that they invest a little of their money. Nobody did. 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