If I put in a limit order for the same price and size as someone else, which order goes through?
The one whose order gets to the exchange first. The exchange receives the orders and arranges them in First-In-First-Out order, by which they're then executed. At some point it is synchronized and put into a list. Whoever gets to that point first - gets the deal. While littleadv's answer is true for many exchanges (in particular the stock market, it's called FIFO matching) you should also know that some markets trade pro rata.  That is, for a match at some price level everyone at that level gets a chunk of the deal proportional to their input (i.e. order size). E.g. match for quantity X at a price level and passive side orders y1, y2; the order y1 would get y1 / (y1 + y2) of X and y2 would get y2 / (y1 + y2)  (for X = min(X, y1 + y2)).
No, this isn't possible, especially not when you're trading a highly liquid stock like Apple. When you put in your buy order at $210, any other traders that have open limit sell orders with the correct parameters, e.g. price and volume, will have their order(s) filled. This will occur before you can put in your own sell order and purchase your own shares because the other orders are listed on the order book first. In the US, many tax-sheltered accounts like IRA's have specific rules against self-dealing, which includes buying and selling assets with yourself, so such a transaction would be prohibited by definition. Although I'm not entirely sure if this applies to stocks, the limitation described in the first paragraph still applies regardless. If this were possible, rest assured that high-frequency traders would take advantage of this tactic to manipulate share prices. (I've heard critics say that this does occur, but I haven't researched it myself or seen any data about it) Not to be a jerk, since I'm learning about options myself, but I think you have a few things wrong about your tesla put postion.  First, assuming it was itm or atm within a week of strike it would maybe be worth $12-15, I glanced at the 11/10 put strikes ~325 trades for $12.65 https://www.barchart.com/stocks/quotes/TSLA/options?expiration=2017-11-10  The closer it gets to expiry theta decay reduces put value significantly, the 325's that expire tomorrow are only worth $2.60.   Expecting TSLA to drop from 325 to 50 a share by Jan has a .006% chance of occuring according to the current delta. It's a lottery ticket at best.  _____ Lastly the $50 price is the expected share price at the date of expiry. The price you pay is 57c for the options. So in order to get to your 494k number TSLA would need to decline $50 dollars to a price of 275 a share. You wouldn't want to buy 50 dollar puts, just the 275 puts, provided it declines very quickly.   EDIT: I was looking at the recent expiration to get an idea of atm or itm prices, since it's not like you would hold to expiration. Also the Jan has a 0.6% chance of hitting 50, not .006%. That said what I've noticed when things start to slide is that puts have a weird way of pricing themselves. For example when something gradually goes up all of the calls go up down the chain through time frames, but puts do not in the same fashion. Further out lower priced puts won't move nearly as much unless the company is basically headed for bankruptcy. "If you really believe in the particular stocks, then don't worry about their daily price.  Overall if the company is sound, and presumably paying a dividend, then you're in it for the long haul. Notwithstanding that, it is reasonable to look for a way out.  The two you describe are quite different in their specifics. Selling sounds like the simpler of the two, but the trigger event, and if it is automatic or ""manual"" matters.  If you are happy to put in a sell order at some time in the future, then just go ahead with that. Many brokers can place a STOP order, that will trigger on a certain price threshold being hit.  Do note, however, that by default this would place a market order, and depending on the price that breaks through, in the event of a flash crash, depending on how fast the brokers systems were, you could find yourself selling quite cheaply. A STOP LIMIT order will place a limit order at a triggered price.  This would limit your overall downside loss, but you might not sell at all if the market is really running away. Options are another reasonable way to deal with the situation, sort of like insurance.  In this case you would likely buy a PUT, which would give you the right, but not the obligation to sell the stock at the price the that was specified in the option.  In this case, no matter what, you are out the price of the option itself (hence my allusion to insurance), but if the event never happens then that was the price you paid to have that peace of mind. I cannot recommend a specific course of action, but hopefully that fleshed out the options you have." From your question, I am guessing that you are intending to have stoploss buy order. is the stoploss order is also a buy order ?  As you also said, you seems to limit your losses, I am again guessing that you have short position of the stock, to which you are intending to place a buy limit order and buy stoploss order (stoploss helps when when the price tanks). And also I sense that you intend to place buy limit order at the price below the market price. is that the situation?  If you place two independent orders (one limit buy and one stoploss buy). Please remember that there will be situation where two orders also get executed due to market movements. Add more details to the questions. it helps to understand the situation and others can provide a strategic solution. Buy and sell orders always include the price at which you buy/sell. That's how the market prices for stocks are determines. So if you want to place a buy order at 106, you can do that. When that order was fulfilled and you have the stock, you can place a sell order at 107. It will be processed as soon as someone places a buy order at 107. Theoretically you can even place sell orders for stocks you haven't even bought yet. That's called short selling. You do that when you expect a stock to go down in the future. But this is a very risky operation, because when you mispredict the market you might end up owing more money than you invested. No responsible banker will even discuss this with you when you can not prove you know what you are doing. You could always maintain a limit order to sell at a price you're comfortable with. "Well, they don't have to enter a market order. I was just saying that for your benefit.   In practice what will really happen is they'll say to themselves   ""I want ABC for no more than 70.00""  The current bid is at 69.60 They'll use a limit order on 10,000 shares. If anyone offers them more than 70.00 the computer program they're using will not accept.  However, the shares won't be bought all at once. A limit order for 10,000 shares will be spit into 1,000 shares at 69.70 and 10,000 for 69.65  The HFT can then make a reasonable guess someone is buying in bulk. So then the HFT sends out a sell order saying ""10 shares at 70.10"". The guy doesn't want that so they do it over again at 70.09  Eventually they notice when the guy accepts at 70.00  So now they knew this guy is willing to pay that. Then HFT buys all the shares they can. ALL SHARES, not just the amount the guy wants. They buy it all at 69.95, which is higher than the 69.70 the guy just paid or whatever.  They then sell it all back to the guy at 70.00  The guy has no choice because all the shares are now gone. He has to pay his highest price.   Once the guy gets his order the HFT just dumps the rest of the shares back at the price they bought them at.  edit: Another way to pull this off is to just literally build your own exchange. Then you can do all of this without any clever tricks. You can just outright give yourself preference over everyone else because you can truly decide what order the trades are being executed." Sure. Depending on how you configure your order, it will either be fulfilled partially or wait until it can be fulfilled. You can set a time limit on your order (usually its either 1 day or 60 days, but may vary between brokerages), and allow or disallow partial fulfilment.