Which is the most liquid market for trading?
I would rate index futures, in particular the US index futures (e.g. the S&P 500 future) as the most liquid markets after the forex markets. Depends on how you measure liquidity.  There's papers out there that approach this very question. Measured in order book spreads for a consolidated $100m trade, I'd say the second biggest market is FX swaps, followed or par'd by the money market (government bonds). If you disallow OTC venues, it's most definitely exchange listed government bonds. If, however, you happen to think in terms of sheer volume per time, the most liquid market phase could be considered the NYSE closing auction, as you can move billions in a matter of minutes, or expressed in speed terms: several m$/s (million dollars per second). You should pick a definition and we can provide you with a more accurate list of candidates and actual data.
I would say it's a bit more complicated than that. Do you understand what a market maker does?  An ECN (electronic communication network) is a virtual exchange that works with market makers. Using a rebate structure that works by paying for orders adding liquidity and charges a fee for removing liquidity. So liquidity is created by encouraging what are essentially limit orders, orders that are outside of the current market price and therefore not immediately executable. These orders stay in the book and are filled when the price of the security moves and triggers them.  So direct answer is NYSE ARCA is where market makers do their jobs. These market makers can be floor traders or algorithmic. When you send an order through your brokerage, your broker has a number of options. Your order can be sent directly to an ECN/exchange like NYSE ARCA, sent to a market making firm like KCG Americas (formerly Knight Capital), or internalized. Internalization is when the broker uses an in house service to execute your trade. Brokerages must disclose what they do with orders. For example etrade's. https://content.etrade.com/etrade/powerpage/pdf/OrderRouting11AC6.pdf This is a good graphic showing what happens in general along with the names of some common liquidity providers. http://www.businessweek.com/articles/2012-12-20/how-your-buy-order-gets-filled Since I've been doing this since late 03 I have colo machines in Chicago and NYC, and have direct exchange data feeds etc.  I mentioned in a prior post though, for someone starting out on algorithmic trading, I'd recommend Nanex for tick data and Interactive Brokers for your brokerage account. IB has a robust and easy to use API. It won't let you do the most low latency stuff bc you can't colo at the exchange and have to clear through their order management systems but if you are looking at opportunities that exist in the market in excess of 50ms it's probably a good place to start. If not, go Lightspeed imo, but that'll cost you on the colo/data a lot more. "This is actually a fairly hard question to answer well as much of the currency trading that is done in financial markets is actually done directly with banks and other financial institutions instead of on a centralized market and the banks are understandably not always excited to part with information on how exactly they do their business.  Other methods of currency exchange have much, much less volume though so it is important to understand the trading through markets as best as possible. Some banks do give information on how much is traded so surveys can give a reasonable indication of relative volume by currency.  Note the U.S. Dollar  is by far the largest volume of currency traded partially because people often covert one currency to another in the markets by trading ""through"" the Dollar.  Wikipedia has a good explanation and a nicely formatted table of information as well." "Joke warning: These days, it seems that rogue trading programs are the big market makers (this concludes the joke) Historically, exchange members were market makers. One or more members guaranteed a market in a particular stock, and would buy whatever you wanted to sell (or vice-versa). In a balanced market -- one where there were an equal number of buyers and sellers -- the spread was indeed profit for them. To make this work, market makers need an enormous amount of liquidity (ability to hold an inventory of stocks) to deal with temporary imbalances. And a day like October 29, 1929, can make that liquidity evaporate. I say ""historically,"" because I don't think that any stock market works this way today (I was discussing this very topic with a colleague last week, went to Wikipedia to look at the structure of the NYSE, and saw no mention of exchange members as market makers -- in fact, it appears that the NYSE is no longer a member-based exchange). Instead, today most (all?) trading happens on ""electronic crossing networks,"" where the spread is simply the difference between the highest bid and lowest ask. In a liquid stock, there will be hundreds if not thousands of orders clustered around the ""current"" price, usually diverging by fractions of a cent. In an illiquid stock, there may be a spread, but eventually one bid will move up or one ask will move down (or new bids will come in). You could claim that an entity with a large block of stock to move takes the role of market maker, but it doesn't have the same meaning as an exchange market maker. Since there's no entity between the bidder and asker, there's no profit in the spread, just a fee taken  by the ECN. Edit: I think you have a misconception of what the ""spread"" is. It's simply the difference between the highest bid and the lowest offer. At the instant a trade takes place, the spread is 0: the highest bid equals the lowest offer, and the bidder and seller exchange shares for money. As soon as that trade is completed, the spread re-appears. The only way that a trade happens is if buyer and seller agree on price. The traditional market maker is simply an entity that has the ability to buy or sell an effectively unlimited number of shares. However, if the market maker sets a price and there are no buyers, then no trade takes place. And if there's another entity willing to sell shares below the market maker's price, then the buyers will go to that entity unless the market's rules forbid it." While open interest usually correlates to volume, the mark of liquidity is the bid ask spread. Even when trading options with spreads as large as an ask 2x the bid, a more realistic price that traders are willing to accept lies somewhere in the middle. Any option can easily be exited at intrinsic value: underlying price - exercise price for calls, exercise price - underlying price for puts.  For illiquid options, this will be the best price obtained.  For longer term options, something closer to the theoretical price is still possible. If an underlying is extremely liquid, yet the options aren't quite then options traders will be much more ready to trade at the theoretical price. For exiting illiquid options, small, < 4 contracts, and infrequent, > 30 minute intervals, orders are more likely to be filled closer to the theoretical price; however, if one's sells are the only trades, traders on the other side will take note and accept ever lowering implied volatilities. With knowledge of what traders will accept, it is always more optimal to trade out of options rather than exercise because of the added costs and uncertainty involved with exercising and liquidating. Some liquidity Since you're using IB, and you seem to be an investor not a trader, so you won't notice especially if you walk your orders, but you will suffer the bid/ask spread as everyone else albeit wider.   If buying, the best strategy unless if one is time constrained is to walk the entire bid from the best bid to the best ask.  It is highly likely that someone will hit your order before you hit the best ask.  If they don't, as a long term investor, the few pennies won't make or break you, especially if the price per share is 100 USD equivalent, but it is an excellent habit to form and fun. Since you're buying ETFs, even though your orders are small, you would be adding liquidity to your market, helping it become more efficient because your orders could be used to arbitrage against all of the ETF's holdings, in turn providing liquidity for those holdings. No liquidity This could only be done with an extremely low cost broker like IB because the trading commissions would make it prohibitively expensive. There are huge risks when trading an illiquid security such as VEUR.  EWL would be much less risky thus less expensive. Securities with no liquidity can be traded, but they must be traded very carefully.  In the case of a security that can only attract about 20 shares per day in volume, only single shares should be bid.  The market makers, suffering from a dearth in volume may not even be willing to haggle; therefore, the only recourse is a statistical arbitrageur, who will attempt to profit from the spread between other more liquid versions of the security. Considering the available alternative, VEUR is not recommended to trade. As Chris pointed out in his comment, smaller stock exchanges may use open outcry. There are several exchanges that use open outcry/floor trading in the US, however, although they aren't necessarily stock exchanges.  Having visited the three Chicago exchanges I mentioned, I can personally vouch for their continued use of a trading floor, although its use is declining in all three. BATS CHi-X Europe is a market maker. They provide liquidity to the order books of different kinds of equities on certain exchanges. So the London Stock Exchange lists equities and the order books show the orders of different market participants. Most of those market participants are market makers. They allow others to complete a trade of an equity closer to the price that persons wants, in a faster time period and in larger amounts, than if there were no market makers providing liquidity. Stock markets are supposed to be about investment and providing capital to companies for operations and research.  High frequency trading is only about gaming the market and nothing else.  Arguments that this provides more capital or liquidity don't make any sense because the speed of trading is such that listed companies cannot take advantage and only high frequency traders are served. "In the US there is only one stock market (ignoring penny stocks) and handfuls of different exchanges behind it.  NYSE and NASDAQ are two different exchanges, but all the products you can buy on one can also be bought on the other; i.e. they are all the same market.  So a US equities broker cannot possibly restrict access to any ""markets"" in the US because there is only one. (Interestingly, it is commonplace for US equity brokers to cheat their customers by using only exchanges where they -- the brokers -- get the best deals, even if it means your order is not executed as quickly or cheaply as possible.  This is called payment for order flow and unfortunately will probably take an Act of Congress to stop.) Some very large brokers will have trading access to popular equity markets in other countries (Toronto Stock Exchange, Mexico Stock Exchange, London Stock Exchange) and can support your trades there.  However, at many brokers or in less popular foreign markets this is usually not the case; to trade in the average foreign country you typically must open an account with a broker in that country." "There are basically two different markets for ADRs and ordinary shares. 1) The American market, 2) the ""local"" market. The following is not true for most stocks in ""developed"" markets. But it is often true that the American market (for ADRs) is far more liquid than the local market for ordinary shares of a developing country. For instance, there was a time when the ADRs of Telmex (Telefonos of Mexico) was the fifth most traded stock in the world, after Exxon (before its merger with Mobil), IBM, Microsoft, and A T&T, meaning that it was easy to trade with low fees on the NYSE. It was much harder and slower to buy the local shares of Telmex in Mexico, on the Mexican exchange. Also, the accompanying currency transactions were harder to execute with the ord, because you have to settle in local currency and pay an FX commission. With the ADR, the exchange rate is ""built"" into the (dollar) price, and you settle in dollars." No, it's not even remotely accurate in the current sense. Both markets have counterparties directly executing against one another, and both have auctions. The auction mechanics are different (with NYSE's Specialist/DMM model) but during normal market hours there isn't much difference. "Liquidity is highly correlated to efficiency primarily because if an asset's price is not sampled during the time of a trade, it's price is unknown therefore inefficient.  Past prices can be referenced, but they are not the price of the present.  Prices of substitutes are even worse. SPY is extremely efficient for an equity.  If permitted, it could easily trade with much lower ticks and still have potential for a locked market. Ideal exchange An ideal exchange has no public restrictions on trade.  This is not to say that private restrictions would need to be put in place for various reasons, but one would only do that if it were responsible for its own survival instead of being too big to fail. In this market, trades would be approximately continuous for the largest securities and almost always locked because of continuous exchange fee competition with ever dropping minimum ticks. A market that can provide continuous locked orders with infinite precision is perfectly efficient from the point of view of the investor because the value of one's holdings are always known. EMH In terms of the theory the Efficient Market Hypothesis this is irrelevant to the rational investor. The rational investor will invest in the market at large of a given asset class, only increasing risk as wealth increases thus moving to more volatile asset classes when the volatility can be absorbed by excess wealth. Here, liquidity is also helpful, the ""two heads are better than one"" way of thinking.  The more invested in an asset class, the lower the class's variance and vice versa.  Bonds, the least variant, dwarf equities which dwarf options, all in order of the least variance.  Believe it or not, there was a day when bonds were almost as risky as equities. For those concerned with EMH, liquidity is also believed to increase efficiency in some forms because liquidity is proportional to the number of individuals invested thus reducing the likelihood of an insufficient number of participants. External inefficiency In the case of ETFs that do not perfectly track their underlying index less costs at all times between index changes, this is because they are forbidden from directly trading in the market on their own behalf. If they were allowed and honest, the price would always be perfect and much more liquid than it otherwise should be since the combined frequency of all index members is much higher than any one alone. If one was dishonest, it would try to defraud with higher or lower numbers; however, if insider trading were permitted, both would fail due to the prisoner's dilemma that there is no honor among thieves.  Here, the market would detect the problem much sooner because the insiders would arbitrage the false price away.   Indirect internal efficiency Taking emerging market ETFs as an example, the markets that those are invested into are heavily restricted, so their ETF to underlying price inefficiencies are more pronounced even though the ETFs are actually working to make those underlying markets more efficient because a price for them altogether is known." This has never really adequately explained it for me, and I've tried reading up on it all over the place. For a long time I thought that in a trade, the market maker pockets the spread *for that trade*, but that's not the case.  The only sensible explanation I've found (which I'm not going to give in full...) is that the market maker will provide liquidity by buying and selling trades they have no actual view on (short or long), and if the spread is higher, that contributes directly to the amount they make over time when they open and close positions they've made.  It would be great to see a single definitive example somewhere that shows how a market maker makes money. Thank you for the comment,  New markets open and close all the time, its interesting seeing the new characters appear here as a certain country demands a supply of a new certain product. You feel a bit ahead of the trends here sometimes in that respect.  Thanks