Which type of stock order would I use to sell a stock that hits a price or drops below it?
A trailing stop will sell X shares at some percentage below the current market price.  Putting in this order with a 10% trailing stop when the stock price is $50 will sell the stock when it hits $45.  It's a market order at that point (see below). A stop order will sell the stock when it reaches a certain price.  The stop order becomes a market order when the magic price is hit.  This means that you may not sell it at or below your price when the order is executed.  But the stock will sell faster because the trader must execute. A stop limit order is the same as a stop order, except the stock won't be sold if it can't be gotten for the price.  As a result, the sell may not be executed. More information here.
"Aganju has mentioned put options, which are one good possibility. I would suggest considering an even easier strategy: short selling.  Technically you are borrowing the stock from someone and selling it.  At some point you repurchase the stock to return to the lender (""covering your short"").  If the stock price has fallen, then when you repurchase it, it will be cheaper and you keep the profit. Short selling sounds complicated but it's actually very easy--your broker takes care of all the details.  Just go to your brokerage and click ""sell"" or ""sell short.""  You can use a market or limit order just like you were selling something you own.  When it sells, you are done.  The money gets credited to your account.  At some point (after the price falls) you should repurchase it so you don't have a negative position any more, but your brokerage isn't going to hassle you for this unless you bought a lot and the stock price starts rising.  There will be limits on how much you can short, depending on how much money is in your account.  Some stocks (distressed and small stocks) may sometimes be hard to short, meaning your broker will charge you a kind of interest and/or may not be able to complete your transaction. You will need a margin account (a type of brokerage account) to either use options or short sell.  They are easy to come by, though. Note that for a given amount of starting money in your account, puts can give you a much more dramatic gain if the stock price falls.  But they can (and often do) expire worthless, causing you to lose all money you have spent on them.  If you want to maximize how much you make, use puts.  Otherwise I'd short sell. About IPOs, it depends on what you mean.  If the IPO has just completed and you want to bet that the share price will fall, either puts or short selling will work.  Before an IPO you can't short sell and I doubt you would be able to buy an option either. Foreign stocks?  Depends on whether there is an ADR for them that trades on the domestic market and on the details of your brokerage account.  Let me put it this way, if you can buy it, you can short sell it." I don't have all the answers. On a illiquid stock, such situations do arise and there are specific mechanisms used by exchanges to match the order. It is generally not advisable to use market order on illiquid stock. There are lots of different variations here. I guess this comes down to specifications for individual exchanges, but I'm wondering if there's a standard here or a way to approach it from basic rules that clears up all these situations. There are quite a few variations and different treatments. Market order that are placed when the market is closed or just around market opening are traded at Market Open price that each exchange has a formulae to calculate. In the process Market Buy are matched to Market Sell at the Exchange calculated price. Not all order get matched and there could be spill over's. These are then matched to limit orders. Is this determined based on which sell order came first, or based on which would result in the best deal for the incoming buyer? Generally Market orders have highest priority of execution. "In general, there should be a ""liquidity premium"" which means that less-liquid stocks should be cheaper. That's because to buy such a stock, you should demand a higher rate of return to compensate for the liquidity risk (the possibility that you won't be able to sell easily). Lower initial price = higher eventual rate of return. That's what's meant when Investopedia says the security would be cheaper (on average). Is liquidity good? It depends. Here's what illiquidity is. Imagine you own a rare piece of art. Say there are 10 people in the world who collect this type of art, and would appreciate what you own. That's an illiquid asset, because when you want to sell, maybe those 10 people aren't buying - maybe they don't want your particular piece, or they all happen to be short on funds. Or maybe worse, only one of them is buying, so they have all the negotiating leverage. You'll have to lower your price if you're really in a hurry to sell. Maybe if you lower your price enough, you can get one of the 10 buyers interested, even if none were initially. An illiquid asset is bad for sellers. Illiquid means there aren't enough buyers for you to get a bidding war going at the time of your choosing. You'll potentially have to wait around for buyers to turn up, or for a stock, maybe you'd have to sell a little bit at a time as buyers want the shares. Illiquid can be bad for buyers, too, if the buyer is for some reason in a hurry; maybe nobody is selling at any given time. But, usually buyers don't have to be in a hurry. An exception may be if you short sell something illiquid (brokers often won't let you do this, btw). In that case you could be a forced buyer and this could be very bad on an illiquid security. If there are only one or two sellers out there, they now have the negotiating leverage and they can ask whatever price they want. Illiquidity is very bad when mixed with margin or short sales because of the potential for forced trades at inopportune times. There are plenty of obscure penny stocks where there might be only one or two trades per day, or fewer. The spread is going to be high on these because the bids at a given time will just be lowball offers from buyers who aren't really all that interested, unless you want to give your stock away, in which case they'll take it. And the asks are going to be from sellers who want to get a decent price, but maybe there aren't really any buyers willing to pay, so the ask is just sitting there with no takers. The bids and asks may be limit orders that have been sitting open for 3 weeks and forgotten about. Contrast with a liquid asset. For example, a popular-model used car in good condition would be a lot more liquid than a rare piece of art, though not nearly as liquid as most stocks. You can probably find several people that want to buy it living nearby, and you're not going to have to drop the price to get a buyer to show up. You might even get those buyers in a bidding war. From illiquid penny stocks, there's a continuum all the way up to the most heavily-traded stocks such as those in the S&P500. With these at a given moment there will be thousands of buyers and sellers, so the spread is going to close down to nearly zero. If you think about it, just statistically, if there are thousands of bids and thousands of asks, then the closest bid-ask pair is going to be close together. That's a narrow spread. While if there are 3 bids and 2 asks on some illiquid penny stock, they might be dollars away from each other, and the number of shares desired might not match up. You can see how liquidity is good in some situations and not in others. An illiquid asset gives you more opportunity to get a good deal because there aren't a lot of other buyers and sellers around and there's some opportunity to ""negotiate"" within the wide spread. For some assets maybe you can literally negotiate by talking to the other party, though obviously not when trading stocks on an exchange. But an illiquid asset also means you might get a bad deal, especially if you need to sell quickly and the only buyers around are making lowball offers. So the time to buy illiquid assets is when you can take your time on both buying and selling, and will have no reason for a forced trade on a particular timeline. This usually means no debt is involved, since creditors (including your margin broker) can force you to trade. It also means you don't need to spend the money anytime soon, since if you suddenly needed the money you'd have a forced trade on your hands. If you have the time, then you put a price out there that's very good for you, and you wait for someone to show up and give you that price - this is how you get a good deal. One more note, another use of the term liquid is to refer to assets with low or zero volatility, such as money market funds. An asset with a lot of volatility around its intrinsic or true value is effectively illiquid even if there's high trade volume, in that any given point in time might not be a good time to sell, because the price isn't at the right level. Anyway, the general definition of a liquid investment is one that you'd be comfortable cashing out of at a moment's notice. In this sense, most stocks are not all that liquid, despite high trading volume. In different contexts people may use ""liquid"" in this sense or to mean a low bid-ask spread." It's actually quite simple. You're actually confusing two concept. Which are taking a short position and short selling itself. Basically when taking a short position is by believing that the stock is going to drop and you sell it. You can or not buy it back later depending on the believe it grows again or not. So basically you didn't make any profit with the drop in the price's value but you didn't lose money either.  Ok but what if you believe the market or specific company is going to drop and you want to profit on it while it's dropping. You can't do this by buying stock because you would be going long right? So back to the basics. To obtain any type of profit I need to buy low and sell high, right? This is natural for use in long positions. Well, now knowing that you can sell high at the current moment and buy low in the future what do you do? You can't sell what you don't have. So acquire it. Ask someone to lend it to you for some time and sell it. So selling high, check.  Now buying low? You promised the person you would return him his stock, as it's intangible he won't even notice it's a different unit, so you buy low and return the lender his stock. Thus you bought low and sold high, meaning having a profit. So technically short selling is a type of short position. If you have multiple portfolios and lend yourself (i.e. maintaining a long-term long position while making some money with a short term short-term strategy) you're actually short selling with your own stock. This happens often in hedge funds where multiple strategies are used and to optimise the transaction costs and borrowing fees, they have algorithms that clear (match) long and short coming in from different traders, algorithms, etc. Keep in mind that you while have a opportunities risk associated.  So basically, yes, you need to always 'borrow' a product to be able to short sell it. What can happen is that you lend yourself but this only makes sense if: There could be a number of reasons: The price hit your number ($39.70) but by the time your order hit the market, the price had gone up. Perhaps the stock went up between when you placed the stop loss and when the order was executed. A trailing stop loss will ratchet up: Very simply, the trailing stop maintains a stop-loss order at a precise percentage below the market price (or above, in the case of a short position). The stop-loss order is adjusted continually based on fluctuations in the market price, always maintaining the same percentage below (or above) the market price. The product type and transaction direction are not linked.  When you short sell a stock, you are still dealing with shares of an equity security.  When you take delivery of a bond, you are buying that bond and holding a long position even though it's a debt security. It depends on how you place your stop order and the type of stop orders available from your broker. If you place a stop market order and the following day the stock opens below your stop your stock will be stopped out at or around the opening price, meaning you can potentially end up with quite a large gap. If you place a stop limit order, say you place your stop at $10.00 with a limit price of $9.90, and if the price opens below $9.90, say at $9.50, your limit sell order of $9.90 will be placed onto the market but it will not be executed until the price goes back up to $9.90 or above. The third option is to place a Guaranteed Stop Loss, and as specified you are guaranteed your stop price even if the price gaps down below your stop price. You will be paying an extra fee for the Guaranteed Stop Loss Order, and they are usually mainly available with CFD Brokers (so if you are in the USA you might be out of luck). "Aganju has mentioned put options, which are one good possibility. I would suggest considering an even easier strategy: short selling.  Technically you are borrowing the stock from someone and selling it.  At some point you repurchase the stock to return to the lender (""covering your short"").  If the stock price has fallen, then when you repurchase it, it will be cheaper and you keep the profit. Short selling sounds complicated but it's actually very easy--your broker takes care of all the details.  Just go to your brokerage and click ""sell"" or ""sell short.""  You can use a market or limit order just like you were selling something you own.  When it sells, you are done.  The money gets credited to your account.  At some point (after the price falls) you should repurchase it so you don't have a negative position any more, but your brokerage isn't going to hassle you for this unless you bought a lot and the stock price starts rising.  There will be limits on how much you can short, depending on how much money is in your account.  Some stocks (distressed and small stocks) may sometimes be hard to short, meaning your broker will charge you a kind of interest and/or may not be able to complete your transaction. You will need a margin account (a type of brokerage account) to either use options or short sell.  They are easy to come by, though. Note that for a given amount of starting money in your account, puts can give you a much more dramatic gain if the stock price falls.  But they can (and often do) expire worthless, causing you to lose all money you have spent on them.  If you want to maximize how much you make, use puts.  Otherwise I'd short sell. About IPOs, it depends on what you mean.  If the IPO has just completed and you want to bet that the share price will fall, either puts or short selling will work.  Before an IPO you can't short sell and I doubt you would be able to buy an option either. Foreign stocks?  Depends on whether there is an ADR for them that trades on the domestic market and on the details of your brokerage account.  Let me put it this way, if you can buy it, you can short sell it."