How to understand adding or removing “liquidity” in stock markets with market/non-market orders?
Not all limit orders add liquidity, but all market orders remove liquidity presuming there is liquidity to remove. A liquidity providing order is one that is posted to the limit book. If an order, even a limit order, is filled before being posted to the limit book, it removes liquidity. Liquidity is measured by a balance and abundance of quantities posted on the limit book and the best spread between the lowest ask and the highest bid.
"That article, like almost any article written by a non-expert and quoting only ""research"" from lobbying groups, hugely misses the point. The vast majority of orders that end up being cancelled are cancelled as a standard part of exchanges' official market-maker programs. Each exchange wants you and me to know that it has liquidity -- that when we go to buy or sell some stock, there will be someone waiting on the other side of the trade.  So the exchange pays (via lowered fees or even rebates) hundreds of registered market makers to constantly have orders resting in each product's order book within a few ticks of the current NBBO or the last trade price.  That way, if everyone else should suddenly disappear from the market, you and I will still be able to trade our shares for a price somewhat close to the last trade price. But market makers who are simply acting in this ""backstop"" role don't actually want to have their orders filled, because those orders will almost always lose them money. So as prices rise and fall (as much as tens of times per second), the market makers need to cancel their resting orders (so they don't get filled) and add new ones at new prices (so they meet their obligations to the exchange).  And because the number of orders resting in any given product's order book is vastly larger than the number of actual trades that take place in any given time period, naturally the number of cancellations is also going to hugely outweigh the number of actual trades.  As much as 97% to 3% (or even more). But that's completely fine! You and I don't have to care about any of that.  We almost never need the market makers to be there to trade with us.  They're only there as a backstop.  There's almost always plenty of organic liquidity for us to trade against.  Only in the rare case where liquidity completely dries up do we really care that the registered market makers are there.  And in those cases (ideally) the market makers can't cancel their orders (depending on how well the exchange has set up its market maker program). So, to answer your question, the effect of standard order cancellation on a stock is essentially none.  If you were to visualize the resting orders in a product's book as prices moved up and down, you would essentially see a Gaussian distribution with mean at the last trade price, and it would move up and down with the price.  That ""movement"" is accomplished by cancellations followed by new orders. P.S. As always, keep in mind that your and my orders almost never actually make it to a real stock exchange anymore.  Nowadays they are almost always sent to brokers' and big banks' internal dark pools.  And in there you and I have no idea what shenanigans are going on.  As just one example, dark pools allow their operators and (for a fee) other institutional participants access to a feature called last look that allows them to cancel their resting order as late as after your order has been matched against it! :( Regarding the question in your comment ... If Alice is sending only bona fide orders (that is, only placing an order at time T if, given all the information she has at time T, she truly wants and intends for it to be filled) then her cancellation at a later time actually adds to the effectiveness of and public perception of the market as a tool for price discovery (which is its ultimate purpose). [In the following example imagine that there are no such things as trading fees or commissions or taxes.] Let's say Alice offers to buy AAPL at $99.99 when the rest of the market is trading it for $100.00.  By doing so she is casting her vote that the ""fair value"" of a share of AAPL is between $99.99 and $100.00. After all, if she thought the fair value of a share of AAPL was higher --  say, between $100.00 and $100.01 -- then she should be willing to pay $100.00 (because that's below fair value) and she should expect that other people in the market will not soon decide to sell to her at $99.99. If some time later Alice does decide that the fair value of AAPL is between $100.00 and $100.01 then she should definitely cancel her order at $99.99, for exactly the reason discussed above.  She probably won't get filled at $99.99, and by sitting there stubbornly she's missing out (potentially forever) on the possibility to make a profit. Through the simple act of cancelling her $99.99 order, Alice is once again casting a vote that she no longer thinks that's AAPL's fair value.  She is (very slightly) altering the collective opinion of the entire market as to what a share of AAPL is worth.  And if her cancellation then frees her up to place another order closer to her perceived fair value (say, at $100.00), then that's another vote for her honest optinion about AAPL's price. Since the whole goal of the market is to get a bunch of particpants to figure out the fair value of some financial instrument (or commodity, or smart phone, or advertising time, etc.), cancellations of honest votes from the past in order to replace them with new, better-informed honest votes in the present can only be a good thing for the market's effectiveness and perceived effectiveness. It's only when participants start sending non-honest votes (non bona fide orders) that things start to go off the rails.  That's what @DumbCoder was referring to in his comment on your original question." "Money market accounts, insured in the same way as other deposits, are strange hybrids of traditional bank deposits and bond mutual funds. Because of the high inflation of the 1970s, banks were starved of deposits and could not produce loans at sufficient rates.  For this reason, they desired a way to fund loans, and Congress enacted the Depository Institutions Deregulation and Monetary Control Act which permitted a new form of account that retained the functionality of a deposit account, such as checking and now electronic transfers, yet transferred the risk to the account thus most of the profit.  This allowed banks to fund each others' new loans through packaging them into asset backed securities to be held in these special accounts. As an added ""protection"", they are not permitted to carry a market value less than what's owed to depositors and are forcibly liquidated and paid in such event.  This is a rare occurrence because of the nature of the assets held: credit assets such as commercial paper, mortgages, and corporate bonds.  This is the opposite case of deposits because so long as a bank can maintain payments on its liabilities and satisfy a few other regulatory requirements, non-regulation satisfying assets could theoretically carry a zero balance, meaning that a bank could owe depositors more than what could be paid by liquidating all assets. Money market accounts will typically pay a higher rate because of their structure.  While inflation is low and immediate term interest rates set by the central bank are also low, the net figure will not appear high, but the ratio will be fantastic, usually something like 3x. The one downside to money market accounts is that withdrawals are restricted by frequency.  This is not such a problem as before since brokerages are now issuing debit cards tied to brokerage accounts, and excess money can be ""swept"" into money market accounts, bypassing the regulatory restriction. In short, money market accounts are currently a far better choice than traditional checking accounts but pay less than savings accounts." "NASDAQ has Pre and After market : NASDAQ Trading Schedule Regular Trading Session Schedule The NASDAQ   Stock Market Trading Sessions (Eastern Time) Pre-Market Trading Hours from 4:00 a.m. to 9:30 a.m.   Market Hours from 9:30 a.m. to 4:00 p.m.   After-Market Hours from 4:00 p.m. to 8:00 p.m.   Quote and order-entry from 4:00 a.m. to 8:00 p.m.   Quotes are open and firm from 4:00 a.m. to 8:00 p.m. You can trade in Pre/After Market but liquidity is very low. If an ""unexpected world events"" occurs, the volume/liquidity will most certainly increase. Another example is the Forex Market that's open 24/7 around the world. As one major forex market closes, another one opens. According to GMT,   for instance, forex trading hours move around the world like this:   available in New York between 01:00 pm – 10:00 pm GMT; at 10:00 pm GMT   Sydney comes online; Tokyo opens at 00:00 am and closes at 9:00 am   GMT; and to complete the loop, London opens at 8:00 am and closes at   05:00 pm GMT. This enables traders and brokers worldwide, together   with the participation of the central banks from all continents, to   trade online 24 hours a day. src" Traders sometimes look at the depth of the book (number of outstanding limit orders) to try and gauge the sentiment of the market or otherwise use this information to formulate their strategy.  If there was a large outstanding buy order at $49.50, there's a decent chance this could increase the price by influencing other traders. However, a limit order at $2 is like an amazon.com price of $200,000 for a book.  It's so far away from realistic that it is ignored.  People would think it is an error. Submitting this type of order is perfectly legal.  If the stock is extremely thinly traded, it might even be encouraged because if someone wanted to sell a bunch and did a really bad job of it, the price could conceivably fall that far and the limit order would be adding liquidity.  I guess.  Your example is pretty extreme. It is not uncommon for there to be limit orders on the book that are not very close to the trading price.  They just sit around.  The majority of trades are done by algorithmic traders and institutional traders and they don't tend to do this, but a retail investor may choose to submit an order like that, just hoping against hope. Also, buy orders are not likely to push prices down, no matter what their price is.  A sell order, yes (even if it isn't executed). "I'll skip the ""authorizing...."" and go right to uses of new shares: Companies need stock as another liquid asset for a variety of purposes, and if not enough stock is available, then may be forced to the open market to acquire, either by exchanging cash or taking on debt to get the cash." It's a covered call.  When I want to create a covered call position, I don't need to wait before the stock transaction settles. I enter it as one trade, and they settle at different times. In general stock markets are very similar to that, however, you can also put in limit orders to say that you will only buy or sell at a given price. These sit in the market for a specified length of time and will be executed when an order arrives that matches the price (or better). Traders who set limit orders are called liquidity (or price) makers as they provide liquidity (i.e. volume to be traded) to be filled later. If there is no counterparty (i.e. buyer to your seller) in the market, a market maker; a large bank or brokerage who is licensed and regulated to do so, will fill your order at some price. That price is based on how much volume (i.e. trading) there is in that stock on average. This is called average daily volume (ADV) and is calculated over varying periods of time; we use ADV30 which is the 30 day average. You can always sell stocks for whatever price you like privately but a market order does not allow you to set your price (you are a price taker) therefore that kind of order will always fill at a market price. As mentioned above limit orders will not fill until the price is hit but will stay on book as long as they aren't filled, expired or cancelled. "As an exercise, I want to give this a shot.  I'm not involved in a firm that cares about liquidity so all this stuff is outside my purview.  As I understand it, it goes something like this: buy side fund puts an order to the market as a whole (all or most possibly exchanges).  HFTs see that order hit the first exchange but have connectivity to exchanges further down the pipe that is faster than the buy side fund.  They immediately send their own order in, which reaches exchanges and executes before the buy side fund's order can.  They immediately put up an ask, and buy side fund's order hits that ask and is filled (I guess I'm assuming the order was a market order from the beginning).  This is in effect the HFT front running the buy side fund.    Is this accurate?  Even if true, whether I have a genuine issue with this... I'm not sure.  Has anyone on the ""pro-HFT"" side written a solid rebuttal to Lewis and Katsuyama that has solid research behind it?"