Is the best ask price the ask at the “top” of the order book? What is the “top” of the book?
The best ask is the lowest ask, and the best bid is the highest bid.  If the ask was lower than the bid then they crossed, and that would be a crossed market and quickly resolved. So the bid will almost always be cheaper than the ask. A heuristic is that a bid is the revenue of the stock at any given time while the ask is the cost, so the market will only ever offer a profit to itself not to the liquidity seeker. If examining the book vertically, all orders are usually sorted descending. Since the best ask is the lowest ask, it is on the bottom of the asks, and vice versa for the best bid. The best bid & best ask will be those closest since that's the narrowest spread and price-time priority will promise that a bid that crosses the asks will hit the lowest ask, the best possible price for the bidder and vice versa for an ask that crosses the best bid. "You're confusing a specific visual representation of the top bid & ask orders selected from the order book with the actual ""top of the book"".  ""Top"" in the sense of the ""top of the book"" is a ranking (by order of ""best"", different for bids vs. asks) and not meant to be strictly a visual positioning on a page or screen. The data in the visual representation comes from the top of the order book (the best bids, and the best asks), but that visual representation is choosing to present it in a specific way. Think of the ""book"" as the model, the abstract collection of outstanding bid and ask order data.  When people talk about the ""top of the book"", they're talking about the best bids (higher being better), and the best asks (lower being better). The visual representation above is but one possible way to render a tip-of-the-iceberg view of the best orders in the ""book"".  The advantage of that particular visual representation is that one can see the asks & bids converging towards the center.  The spread is visible as the difference between the two middle elements – being the lowest row in the blue ""Asks"" area, and the highest row in the green ""Bids"" area. The up-arrow they had included in the ""Asks"" area was perhaps meant to provide a clue about how the data was sorted contrary to expectations of descending order of ""bestness"", and/or to imply there is further depth to the book data in the indicated direction. If the bids & asks had been oriented side-by-side instead, they might have chosen to represent it as below, re-arranging the rows in the ""Asks"" in the opposite order (i.e. in the order you had expected) so that the ""bests"" are both in the top row:"
From the non-authoritative Investopedia page: A stop-limit order will be executed at a specified price, or better, after a given stop price has been reached. Once the stop price is reached, the stop-limit order becomes a limit order to buy or sell at the limit price or better. So once the stop price has been breached, your limit order is placed and will be on the order books as a $9 ask. For a vanilla stop order, a market order will be placed and will be filled using the highest active bid(s). 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. "- In a quote driven market, must every investor trade with a market        maker? In other words, two parties that are both not market makers        cannot trade between themselves directly? In a way yes, all trades go through a market maker but those trades can be orders put in place by a ""person"" IE: you, or me. - Does a quote driven market only display the ""best"" bid and ask        prices proposed by the market makers? In other words, only the        highest bid price among all the market makers is displayed, and        other lower bid prices by other market makers are not? Similarly,        only the lowest ask price over all market makers is displayed, and        other higher ask prices by other market makers are not? No, you can see other lower bid and higher ask prices. - In a order-driven market, is it meaningful to talk about ""the current stock price"", which is the price of last transaction? Well that's kind of an opinion. Information is information so it won't be bad to know it. Personally I would say the bid and ask price is more important. However in the real world these prices are changing constantly and quickly so realistically it is easier to keep track of the quote price and most likely the bid/ask spread is small and the quote will fall in between. The less liquid a security is the more important the bid/ask is. -- This goes for all market types. - For a specific asset, will there be several transactions happened at    the same time but with different prices? Today with electronic markets, trades can happen so quickly it's difficult to say. In the US stock market trades happen one at a time but there is no set time limit between each trade. So within 1 second you can have a trade be $50 or $50.04. However it will only go to $50.04 when the lower ask prices have been exhausted.   - Does an order driven market have market makers?  By definition, no. - What are some examples of quote driven and order driven financial markets, in which investors are commonly trading stocks and derivatives, especially in U.S.? Quote driven market: Bond market, Forex. Order driven market: NYSE comes from an order driven market but now would be better classified as a ""hybird market"" Conclusion: If you are asking in order to better understand today's stock markets then these old definitions of Quote market or Order market may not work. The big markets in the real world are neither. (IE: Nasdaq, NYSE...) The NYSE and Nasdaq are better classified as a ""hybird market"" as they use more then a single tactic from both market types to insure market liquidity, and transparency. Markets these days are strongly electronic, fast, and fairly liquid in most cases. Here are some resources to better understand these markets: An Introduction To Securities Markets The NYSE And Nasdaq: How They Work Understanding Order Execution" "Realize this is almost a year old, but I just wanted to comment on something in Dynas' answer above...  ""Whenever you trade always think about what the other guys is thinking. Sometimes we forget their is someone else on the other side of my trade that thinks essentially the exact opposite of me. Its a zero sum game."" From a market maker's perspective, their primary goal is not necessarily to make money by you being wrong, it is to make money on the bid-offer spread and hedging their book (and potentially interalize). That being said, the market maker would likely be quoting one side of the market away from top of the book if they don't want to take exposure in that direction (i.e. their bid will be lower than the highest bid available or their offer higher than the lowest offer available). This isn't really going to change anything if you're trading on an exchange, but important to consider if you can only see the prices your broker/dealer provides to you and they are your counterparty in the trade." Based on my research while asking How are unmarketable market orders (other side of the order book is empty) matched with incoming orders? and the one answer there, it seems like there are a few things for certain: All of this of course depends on the exact algorithm specified by the given exchange - I don't think there's a standard here. "During the day, market and limit orders are submitted at any time by market participants and there is a bid and an ask that move around over time.  Trades occur whenever a market order is submitted or a limit order is submitted that at a price that matches or exceeds an existing limit order.  If you submit a market order, it may consume all best-price limit orders and you can get multiple prices, changing the bid or ask at the same time.  All that stuff happens during the trading day only. What happens at the end of the day is different.  A bunch of orders that were submitted during the day but marked as ""on close"" are aggregated with any outstanding limit orders to create a single closing price according to the algorithm established by the exchange.  Each exchange may handle the details of this closing event differently.  For example, the Nasdaq's closing cross or the NYSE's closing auction. The close is the most liquid time of the day, so investors who are trading large amounts and not interested in intraday swings will often submit a market-on-close or limit-on-close order.  This minimizes their chance of affecting the price or crossing a big spread.  It's actually most relevant for smaller stocks, which may have too little volume during the day to make big trades, but have plenty at the close.  In short, the volume you see is due to these on-close orders. The spike in volume most likely has no special information about what will happen overnight or the next day.  It's probably just a normal part of the market for illiquid stocks." yes you are right as per my understanding while doing trade you must consider fol (specially for starters like me) The volume of the stock you are trading in should be high enough to keep you secure for quick in and out Whenever the bid volume is more than the ask volume the prices will move up and vice versa. to give an example if a stock is at 100 points and there are fol bids: The transaction will occur when either the bidder agrees to pay the ask price (case 1. he pays 101 . his bid offer will disappear and the next best ask will be 102. and the current price will be 101 which was the last transaction.) or when the person giving ask price agrees to deal at best bid which was 99 in which case the share will go down. "In addition to the other answers it's also noteworthy that the stock exchanges themselves adjust the price quotes via their ex-div mechanism.  All limit orders present in the book when the stock goes ex-div will be adjusted by the dividend. Which means you can't even get ""accidentally"" filled in the very unlikely case that everyone forgot to adjust their quotes."