Why do stock exchanges close at night?
Here are some plausible reasons why markets might continue to close: I believe there are electronic exchanges that run continuously,  but the older ones don't want to change their practices since some people may have strategies which  (claim they) are based on this behavior so there would be a lot of unhappy people if it was altered. The pause doesn't seem to do any harm. There are alternatives if you dislike it. Don't try to fix what isn't broken. Most stocks are not actively trades by lots of people.   When you buy or sell a stock the price is set by the “order book” – that is the other people looking to trade in the given stock at the same time. Without a large number of active traders, it is very likely the pricing system will break down and result in widely changing prices second by second.   Therefore for the market to work well, it need most people to be trading at the same time.
How come when I sell stocks, the brokerage won't let me cash out for three days, telling me the SEC requires this clearance period for the transaction to clear, but they can swap shit around in under a second?   Be interesting to see what would happen if *every* transaction wasn't cleared until the closing bell. Limited transactions: what's to stop a firm from having thousands of bank accounts to avoid the limit. This of course is costly.   Tax on transactions: some trades are worth $00.001 and some are $190,000. They shouldn't be taxed the same.   Both increase costs of capital and literally everyone in America pays for it. Investment is more expensive. And our beautiful liquid market is no longer as efficient and can no longer responds as quickly to market forces. Investors now go to other foreign markets that don't limit or charge for transactions. Both plans will cost the economy billions of dollars and for what? So some computers don't trade almost instantaneously? Exactly why is that a problem other than class warfare? A lot of the risks that people have about flash crashes have been mitigated with better algorithms and rules. One of the fundamental of technical analysis suggests that holding a security overnight represents a huge commitment.  Therefore it would follow that traders would tend to close their positions prior to market close and open them when it opens. During the 12 plus hours the market was closed news can change investors opinion of the stock. When the market reopens that first trade could be much different than the last trade the day before. Unless you want to be a short term day trader, then it is not foolish to be an end of day trader. If you are looking to be a medium to long term trader/investor then it is quite acceptable to put orders in after market close. Some would say it is even less risky, because you are not watching the price fluctuate up and down and letting your emotions getting the best of you. The NYSE holidays are listed online here: https://www.nyse.com/markets/hours-calendars If it was typical, above the board, and no profits were made, then why did it take a hotly contested bill from Congress (that was amended and watered down) to bring these transactions to light?  Why not just use the normal discount window for these overnight loans if everything was just run of the mill overnight loans?   Why were they making these standard 0% overnight loans to select private investors? The two answers so far are right, but there's a third factor - for many stocks, there's after hours trading. So the official 4PM close is not what the stock's last trade was when they open again. Regardless, even that after hour price is not the starting point as Muro points out. The opening price is derived from new information received. It reflects the current state of the market. Opening Price Deviation (from Investopedia): Investor expectation can be changed by corporate announcements or   other events that make the news. Corporations typically make   news-worthy announcements that may have an effect on the stock price   after the market closes. Large-scale natural disasters or man-made   disasters such as wars or terrorist attacks that take place in the   afterhours may have similar effects on stock prices. When this   happens, some investors may attempt to either buy or sell securities   during the afterhours. Not all orders are executed during after-hours trading. The lack of   liquidity and the resulting wide spreads make market orders   unattractive to traders in after-hours trading. This results in a   large amount of limit or stop orders being placed at a price that is   different from the prior day’s closing price. Consequently, when the   market opens the next day, a substantial disparity in supply and   demand causes the open to veer away from the prior day’s close in the   direction that corresponds to the effect of the announcement, news or   event. You seem to think that stock exchanges are much more than they actually are. But it's right there in the name: stock exchange. It's a place where people exchange (i.e. trade) stocks, no more and no less. All it does is enable the trading (and thereby price finding). Supposedly they went into mysterious bankruptcy then what will happen to the listed companies  Absolutely nothing. They may have to use a different exchange if they're planning an IPO or stock buyback, that's all. and to the shareholder's stock who invested in companies that were listed in these markets ?  Absolutley nothing. It still belongs to them. Trades that were in progress at the moment the exchange went down might be problematic, but usually the shutdown would happen in a manner that takes care of it, and ultimately the trade either went through or it didn't (and you still have the money). It might take some time to establish this. Let's suppose I am an investor and I bought stocks from a listed company in NYSE and NYSE went into bankruptcy, even though NYSE is a unique business, meaning it doesn't have to do anything with that firm which I invested in. How would I know the stock price of that firm  Look at a different stock exchange. There are dozens even within the USA, hundreds internationally. and will I lose my purchased stocks ?  Of course not, they will still be listed as yours at your broker. In general, what will happen after that ?  People will use different stock exchanges, and some of them migth get overloaded from the additional volume. Expect some inconveniences but no huge problems. "Firstly, if a stock costs $50 this second, the bid/ask would have to be 49/50.  If the bid/ask were 49/51, the stock would cost $51 this second.  What you're likely referring to is the last trade, not the cost.  The last trading price is history and doesn't apply to future transactions. To make it simple, let's define a simple order book.  Say there is a bid to buy 100 at $49, 200 at $48, 500 at $47.  If you place a market order to sell 100 shares, it should all get filled at $49.  If you had placed a market order to sell 200 shares instead, half should get filled at $49 and half at $48.  This is, of course, assuming no one else places an order before you get yours submitted.  If someone beats you to the 100 share lot, then your order could get filled at lower than what you thought you'd get.  If your internet connection is slow or there is a lot of latency in the data from the exchange, then things like this could happen.  Also, there are many ECNs in addition to the exchanges which may have different order books.  There are also trades which, for some reason, get delayed and show up later in the ""time and sales"" window. But to answer the question of why someone would want to sell low... the only reason I could think is they desire to drive the price down." The shift to trading at the close began in 2008. Traders did not want to be caught off guard by surprise news and there was a lot of volatility during the financial crisis, so they would close their position in the evening. Thats how it began. There are two reasons why it sticks around. First, there has been an increase usage of index funds or passive funds. These funds tend to update their positions at the end of the day. From the WSJ: Another factor behind the shift has been the proliferation of passively managed investments, such as index funds. These funds aim to mimic an index, like the S&P 500, by owning the shares that comprise it. Index funds don’t trade as often as active investors, but when they do, it is typically near the market close, traders say. That is because buying or selling a stock at its closing price better aligns their performance with the index they are trying to emulate. The second reason is simply that volume attracts volume. As a result of whats mentioned above, you have a shift to end of day trading, and the corrolary to that is that there is a liquidity shortage from 10am to 3pm. Thus, if you want to buy or sell a stock, but there are few buyers or sellers around, you will significant move the price when you enter your order. Obviously this does not affect retail traders, but imagine hedge funds entering or closing a billion dollar position. It can make a huge impact on price. And one way to mitigate that is to wait until there are more market participants to take the other end of your trade, just as at the end of the day. So this is a self-reinforcing trend that has begun in the markets and will likely stick around. http://www.wsj.com/articles/traders-pile-in-at-the-close-1432768080 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. "There are quite a few regulations on ""Insider Trading"". Blackouts are one of the means companies adopt to comply with ""Insider Trading"" regulations, mandating employees to refrain from selling/buying during the notified period. Once you leave the employment: So unless there is an urgent need for you to sell/buy the options, wait for some time and then indulge in trade." I understand the question, I think. The tough thing is that trades over the next brief time are random, or appear so. So, just as when a stock is $10.00 bid / $10.05 ask, if you place an order below the ask, a tick down in price may get you a fill, or if the next trades are flat to higher, you might see the close at $10.50, and no fill as it never went down to your limit.  This process is no different for options than for stocks.  When I want to trade options, I make sure the strike has decent volume, and enter a market order. Edit - I reworded a bit to clarify. The Black–Scholes is a model, not a rigid equation. Say I discover an option that's underpriced, but it trades under right until it expires. It's not like there's a reversion to the mean that will occur. There are some very sophisticated traders who use these tools to trade in some very high volumes, for them, it may produce results. For the small trader you need to know why you want to buy a stock or its option and not worry about the last $0.25 of its price.