How is the actual trade on exchanges processed for simple stock orders?
"The simple answer is, there are many ways for trades to take place.  Some systems use order-matching software that employs proprietary algorithms for deciding the order of processing, others use FIFO structures, and so on.  Some brokerages may fill customer orders out of their own accounts (which happens more frequently than you might imagine), and others put their orders into the system for the market makers to handle.  There's no easy all-encompassing answer to your question, but it's still a good one to ask. By the way, asking if the market is ""fair"" is a bit naive, because fairness depends on what side of the trade you came out on! (grin)  If your limit order didn't get filled and you missed out on an opportunity, that's always going to seem unfair, right?"
It's not primarily more people investing. In the 1980s stock exchanges went from open outcry trading floors where all trades involved actually exchanging pieces of paper to electronic trading. Once that happened, it wasn't long before most trades were executed by computer programs rather than human beings, turning stocks over rapidly for very short-term profits rather than long-term investment, greatly increasing  the number of trades (and also increasing liquidity for the actual investors; it's by no means all bad). "* Claiming something is a simple solution does not make it a simple solution * Taxation is not a simple solution * Taxing HFT is just going to cause the HFT traders to squish around and find loopholes and ways to avoid the letter of the law, making the situation *more complicated* * This will engender *more* legislation, further obfuscating the market, making it even harder to understand exactly what's happening * And on and on the cycle goes, the government with ""simple"" solutions that don't work, and the market responding by squeezing around them somehow  Here's a better way to solve this: ***STOP TRADING ON A MARKET YOU DO NOT TRUST!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!***  Don't ask the government to step in and clean it up. JUST FUCKING STOP USING IT! Make a new exchange, an exchange that *chooses* to not allow HFT, and let the HFT-inclusive markets collapse into a shitpool of cancelled block orders that nobody can use.  *THAT* is the simple solution - let it fall apart on its own. *Let it die a death of natural causes!* But that solution does not empower the government or accord it a ""right"" to tax something, so *that* solution will *never* be discussed, nor implemented." "I recommend avoiding trading directly in commodities futures and options.  If you're not prepared to learn a lot about how futures markets and trading works, it will be an experience fraught with pitfalls and lost money – and I am speaking from experience. Looking at stock-exchange listed products is a reasonable approach for an individual investor desiring added diversification for their portfolio.  Still, exercise caution and know what you're buying. It's easy to access many commodity-based exchange-traded funds (ETFs) on North American stock exchanges.  If you already have low-cost access to U.S. markets, consider this option – but be mindful of currency conversion costs, etc. Yet, there is also a European-based company, ETF Securities, headquartered in Jersey, Channel Islands, which offers many exchange-traded funds on European exchanges such as London and Frankfurt.  ETF Securities started in 2003 by first offering a gold commodity exchange-traded fund. I also found the following: London Stock Exchange: Frequently Asked Questions about ETCs.  The LSE ETC FAQ specifically mentions ""ETF Securities"" by name, and addresses questions such as how/where they are regulated, what happens to investments if ""ETF Securities"" were to go bankrupt, etc. I hope this helps, but please, do your own due diligence." "Stock price is set to the price with the highest transaction volume at any given time.  The stock price you cited was only valid in the last transaction on a specific stock exchange. As such it is more of an ""historic"" value. Next trade will be done with the next biggest volume. Depending on the incoming bids and asks this could be higher or lower, but you can assume it will not be too far off if there is no crash underway. Simple example stock exchange:" "I place a trade, a limit order on a thinly traded stock. I want to buy 1000 shares at $10. The current price is $10.50. Someone places a market order for 500 shares. Another trader has a limit order for $10.10 for 400 shares. His order fills, and I get 100 at my price. I wait another day to see if I get any more shares. This is just an example of how it can work. I can place my order as ""all or none"" if I wish to avoid this." They are providing you a service and they charge you for it. The service includes giving you a trading platform(website and the infrastructure), doing all the background work for setting up services for you, relaying your orders to the market or as a broker fulfilling your orders, doing settlement when an order is matched, giving you access to the stock market(the costs are quite high to get a license to relay orders to the market and I believe it needs to be renewed every year). There are transaction fees which the stock exchanges charge the brokers to use the stock markets infrastructure and connect to it. And then interfacing with banks for monetary transactions and also doing according to the law in the jurisdiction they are located in. Most of it is an one time cost, but they are a private enterprise out to make profit so they will charge for their services. Futures exchanges are essentially auction houses facilitating a two-way auction. While they provide a venue for buyers and sellers to come together and transact (be that a physical venue such as a pit at the CME or an electronic network such as Globex), they don't actively seek out or find buyers and sellers to pair them together. The exchanges enable this process through an order book. As a futures trader you may submit one of two types of order to an exchange: Market Order - this is sent to the exchange and is filled immediately by being paired with a limit order.   Limit Order - this is placed on the books of the exchange at the price you specify. If other participants enter opposing market orders at this price, then their market order will be paired with your limit order. In your example, trader B wishes to close his long position. To do this he may enter a market sell order, which will immediately close his position at the lowest possible buy limit price, or he may enter a limit sell order, specifying the price at or above which he is willing to sell. In the case of the limit order, he will only sell and successfully close his position if his order becomes the lowest sell order on the book. All this may be a lot easier to understand by looking at a visual image of an order book such as the one given in the explanation that I have published here: Stop Orders for Futures Finally, not that as far as the exchange is concerned, there is no difference between an order to open and an order to close a position. They're all just 'buy' or 'sell' orders. Whether they cause you to reduce/exit a position or increase/establish a position is relative to the position you currently hold; if you're flat a buy order establishes a new position, if you're short it closes your position and leaves you flat. "In US public stock markets there is no difference between the actions individual retail traders are ""permitted"" to take and the actions institutional/corporate traders are ""permitted"" to take.  The only difference is the cost of those actions.  For example, if you become a Registered Market Maker on, say, the BATS stock exchange, you'll get some amazing rebates and reduced transaction prices; however, in order to qualify for Registered Market Maker status you have to maintain constant orders in the book for hundreds of equities at significant volumes.  An individual retail trader is certainly permitted to do that, but it's probably too expensive. Algorithmic trading is not the same as automated trading (algorithmic trading can be non-automated, and automated trading can be non-algorithmic), and both can be anywhere from low- to high-frequency.  A low-frequency automated strategy is essentially indistinguishable from a person clicking their mouse several times per day, so: no, from a legal or regulatory perspective there is no special procedure an individual retail trader has to follow before s/he can automate a trading strategy.  (Your broker, on the other hand, may have all sorts of hoops for you to jump through in order to use their automation platform.) Last (but certainly not least) you will almost certainly lose money hand over fist attempting bid-ask scalping as an individual retail trader, whether your approach is algorithmic or not, automated or not.  Why?  Because the only way to succeed at bid-ask scalping is to (a) always be at/near the front of the queue when a price change occurs in your favor, and (b) always cancel your resting orders before they are executed when a price change occurs against you.  Unless your algorithms are smarter than every other algorithm in the industry, an individual retail trader operating through a broker's trading platform cannot react quickly enough to succeed at either of those.  You would have to eschew the broker and buy direct market access to even have a chance, and that's the point at which you're no longer a retail trader. Good luck!"