FOK order type: can they be market or limit orders?
"The SEC reference document (PDF) explains order types in more detail. A fill-or-kill order is neither a market order nor a limit order; instead it's something in between. A market order asks to be filled at the best available price, whatever that price might be when the order gets to the exchange.  Additionally, if there are not enough counterparties to fill the order at the best available price, then part of the order may be filled at a worse price.  This all happens more or less immediately; there's no way to cancel it once it has been placed. A limit order asks to be filled at a particular price, and if no counterparties want to trade at that price right now, then the order will just sit around all day waiting for someone to agree on the price; it can be canceled at any time. A fill-or-kill order asks to be filled at a particular price (like a limit order), but if that price or a better one is not currently available then the order is immediately canceled.  It does not accept a worse price (the way a market order does), nor does it sit around waiting (the way a limit order does).  Since the exchange computes whether to ""fill"" or ""kill"" the order as soon as it is arrives, there's also no way to cancel it (like a market order)." You can do FOK on both market and limit orders. Normal market orders will partial fill if you want more shares than are being offered, or if someone pulled their order before you get there and now there are fewer shares than you placed a trade for. With a FOK limit order not at the BBO you are shooting in the dark for a quick match, most of the time it does not fill.  This is a commonly used order type for UHFT arbitrage.  Some exchanges will not attempt to cross it for a match if its price is not at, or better than the market price. When the FOK limit order is at the BBO it is essentially a FOK market order.   FYI: Sometimes you have a minimum quantity to fill option, so you can let the order sit on the book until it fills or you cancel.
The everyday investor buys at the ask and sells at the bid but the market maker does the opposite This is misleading; it has nothing to do with being either an investor or a market maker. It is dependent on the type of order that is submitted. When a market trades at the ask, this means that a buy market order has interacted with a sell limit order at the limit price. When a market trades at the bid, this means that a sell market order has interacted with a buy limit order at the limit price. An ordinary investor can do exactly the same as a market maker and submit limit orders. Furthermore, they can sit on both sides of the bid and ask exactly as a market maker does. In the days before high frequency trading this was quite common (an example being Daytek, whose traders were notorious for stepping in front of the designated market maker's bid/ask on the Island ECN). An order executes ONLY when both bid and ask meet. (bid = ask) This is completely incorrect. A transaction occurs when an active (marketable) order is matched with a passive (limit book) order. If the passive order is a sell limit then the trade has occurred at the ask, and if it is a buy limit the trade has occurred at the bid. The active orders are not bids and asks. The only exception to this would be if the bid and ask have become crossed. When a seller steps in, he does so with an ask that's lower than the stock's current ask Almost correct; he does so with an order that's lower than the stock's current ask. If it's a marketable order it will fill the front queued best bid, and if it's a limit order his becomes the new ask price. A trade does not need to occur at this price for it to become the ask. This is wrong, market makers are the opposite party to you so the prices are the other way around for them. This is wrong. There is no distinction between the market maker and yourself or any other member of the public (beside the fact that designated market makers on some exchanges are obliged to post both a bid and ask at all times). You can open an account with any broker and do exactly the same as a market maker does (although with nothing like the speed that a high frequency market-making firm can, hence likely making you uncompetitive in this arena). The prices a market maker sees and the types of orders that they are able to use to realize them are exactly the same as for any other trader. Difference between a limit and market order is largely a trade-off between price certainty and timing certainty. If you think the security is already well priced, the downside of a limit order is the price may never hit your limit and keep trading away from you. You'll either spend a lot of time amending your order or sitting around wishing you'd amended your order.  The downside of a market order is you don't know the execution price ahead of time. This is typically more of a issue with illiquid instruments where even smaller orders may have price impact. For small trades in more liquid securities your realized price will often resemble the last traded price. Hope that helps. Both have a purpose, and the best tool for the job will depend on your circumstances. You can make a purchase at the after market price by sending an order that gets executed in after market. Often times these are called Extended orders, or EXT. With an EXT limit order it will place the bid on the after market hours order book. If you get filled, then you have the shares.  This is the answer. The role of the market maker is to make sure there is a bid and ask on a particular stock.  That's it.  The market maker ensures that there is a price at which you can buy and a price at which you can sell immediately, but these are not necessarily the best prices.  The majority of trades do not involve market makers and occur between two third parties. Whoever said a market order trades with the market maker is thinking of the way stock markets were years ago, not the way they are now. Market orders are supposed to execute immediately and at one time trading with the market makers was the method for executing immediately. If you issue a market order today, it executes with the best available limit order(s) on the other wide of the trade.  This may or may not involve a party that identifies as a market maker. The principle of demand-supply law will not work if spoofing (or layering, fake order) is implemented. However, spoofing stocks is an illegal criminal practice  monitored by SEC. In stock market, aggressive buyer are willing to pay for a higher ask price pushing the price higher even if ask size is considerably larger than bid size, especially when high growth potential with time is expected. Larger bids may attract more buyers, further perpetuating a price increase (positive pile-on effect). Aggressive sellers are willing to accept a lower bid price pushing the price lower even if ask size is considerably smaller than bid size, when a negative situation is expected. Larger asks may attract more sellers, further perpetuating a price fall (negative pile-on effect).  Moreover, seller and buyers considers not only price but also size of shares in their decision-making process, along with marker order and/or limit order. Unlike limit order, market order is not recorded in bid/ask size. Market order, but not limit order, immediately affects the price direction. Thus, ask/bid sizes alone do not give enough information on price direction. If stocks are being sold continuously at the bid price, this could be the beginning of a downward trend; if stocks are being sold continuously at the ask price, this could be the beginning of a upward trend.  This is because ask price is always higher than bid price. In all the cases, both buyers and sellers hope to make a profit in a long-term and short-term view I think it all boils down to which is your priority.   So it all depends. People that want the stock sooOoooo badly will definitely go for the market order. In India, as suggested above, short/long position can be taken either in F&O or Spot market. The F&O segment short/long can be kept open for appx. 3 months by taking position on the far contract. In intra-day/Spot market, usually the position has to be squared at the end of day or the broker will square it during expiry (forcibly). However, having said that, it is a broker specific feature, as per National Stock Exchange (NSE) or Bombay Stock Exchange (BSE) any transaction has to be settled at the end of T+2 days (T being the trade day). Some brokers allow intra-day positions to be open for T+1 or T+2 days as long as the margin is provided. This is a broker specific discretion as the actual settlement is on T+2 (or in some cases as the exchange specifies). So, in general, to short a stock for a longer time, F&O segment should be used. Yes for every order there is a buyer and seller. But overall there are multiple buyers and multiple sellers. So every trade is at a different price and this price is agreed by both buyer and seller. Related question will help you understand this better. How do exchanges match limit orders?