Are stocks only listed with one exchange in one place?
"Depends. The short answer is yes; HSBC, for instance, based in New York, is listed on both the LSE and NYSE. Toyota's listed on the TSE and NYSE. There are many ways to do this; both of the above examples are the result of a corporation owning a subsidiary in a foreign country by the same name (a holding company), which sells its own stock on the local market. The home corporation owns the majority holdings of the subsidiary, and issues its own stock on its ""home country's"" exchange. It is also possible for the same company to list shares of the same ""pool"" of stock on two different exchanges (the foreign exchange usually lists the stock in the corporation's home currency and the share prices are near-identical), or for a company to sell different portions of itself on different exchanges. However, these are much rarer; for tax liability and other cost purposes it's usually easier to keep American monies in America and Japanese monies in Japan by setting up two ""copies"" of yourself with one owning the other, and move money around between companies as necessary. Shares of one issue of one company's stock, on one exchange, are the same price regardless of where in the world you place a buy order from. However, that doesn't necessarily mean you'll pay the same actual value of currency for the stock. First off, you buy the stock in the listed currency, which means buying dollars (or Yen or Euros or GBP) with both a fluctuating exchange rate between currencies and a broker's fee (one of those cost savings that make it a good idea to charter subsidiaries; could you imagine millions a day in car sales moving from American dealers to Toyota of Japan, converted from USD to Yen, with a FOREX commission to be paid?). Second, you'll pay the stock broker a commission, and he may charge different rates for different exchanges that are cheaper or more costly for him to do business in (he might need a trader on the floor at each exchange or contract with a foreign broker for a cut of the commission)."
Ending up with nothing is an unlikely situation unless you invest 100% in a company stock and the company goes under. In order to give you a good answer we need to see what options your employer gives for 401k investments. The best advice would be to take a list of all options that your employer allows and talk with a financial advisor. Here are a few options that you may or may not have as an option from an employer: Definitions from wikipedia: A target-date fund – also known as a lifecycle, dynamic-risk or age-based fund – is a collective investment scheme, usually a mutual fund, designed to provide a simple investment solution through a portfolio whose asset allocation mix becomes more conservative as the target date (usually retirement) approaches. An index fund or index tracker is a collective investment scheme (usually a mutual fund or exchange-traded fund) that aims to replicate the movements of an index of a specific financial market... An exchange-traded fund (ETF) is an investment fund traded on stock exchanges, much like stocks.[1] An ETF holds assets such as stocks, commodities, or bonds, and trades close to its net asset value over the course of the trading day. Most ETFs track an index, such as a stock index or bond index. ETFs may be attractive as investments because of their low costs, tax efficiency, and stock-like features. The capital stock (or stock) of an incorporated business constitutes the equity stake of its owners. Which one can you lose everything in? You can lose everything in stocks by the company going under. In Index funds the entire market that it follows would have to collapse. The chances are slim here since the index made up of several companies. The S&P 500 is made up of 500 leading companies publicly traded in the U.S.  A Pacific-Europe index such as MSCI EAFE Index is made up of 907 companies. The chances of losing everything in an ETF are also slim. The ETF that follows the S&P 500 is made up of 500 companies. An Pacific-Europe ETF such as MSCI EAFE ETF is made up of 871 companies. Target date funds are also slim to lose everything. Target date funds are made up of several companies like indexes and etfs and also mix in bonds and other investments depending on your age. What would I recommend? I would recommend the Index funds and/or ETFs that have the lowest fee that make up the following strategy for your age: Why Not Target Date Funds or Stocks? Target date funds have high fees. Later in life when you are closer to retirement you may want to add bonds to your portfolio. At that time if this is the only option to add bonds then you can change your elections. Stocks are too risky for you with your current knowledge. If your company matches by buying their stock you may want to consider reallocating that stock at certain points to your Index funds or ETFs. 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. "Not all call options that have value at expiration, exercise by purchasing the security (or attempting to, with funds in your account).   On ETNs, they often (always?) settle in cash.  As an example of an option I'm currently looking at, AVSPY, it settles in cash (please confirm by reading the documentation on this set of options at http://www.nasdaqomxtrader.com/Micro.aspx?id=Alpha, but it is an example of this).  There's nothing it can settle into (as you can't purchase the AVSPY index, only options on it).  You may quickly look (wikipedia) at the difference between ""American Style"" options and ""European Style"" options, for more understanding here. Interestingly I just spoke to my broker about this subject for a trade execution.  Before I go into that, let me also quickly refer to Joe's answer:  what you buy, you can sell.  That's one of the jobs of a market maker, to provide liquidity in a market.  So, when you buy a stock, you can sell it.  When you buy an option, you can sell it.  That's at any time before expiration (although how close you do it before the closing bell on expiration Friday/Saturday is your discretion).  When a market maker lists an option price, they list a bid and an ask.  If you are willing to sell at the bid price, they need to purchase it (generally speaking).  That's why they put a spread between the bid and ask price, but that's another topic not related to your question -- just note the point of them buying at the bid price, and selling at the ask price -- that's what they're saying they'll do. Now, one major difference with options vs. stocks is that options are contracts. So, therefore, we can note just as easily that YOU can sell the option on something (particularly if you own either the underlying, or an option deeper in the money).  If you own the underlying instrument/stock, and you sell a CALL option on it, this is a strategy typically referred to as a covered call, considered a ""risk reduction"" strategy.  You forfeit (potential) gains on the upside, for money you receive in selling the option. The point of this discussion is, is simply: what one buys one can sell;  what one sells one can buy -- that's how a ""market"" is supposed to work.  And also, not to think that making money in options is buying first, then selling.  It may be selling, and either buying back or ideally that option expiring worthless. -- Now, a final example.  Let's say you buy a deep in the money call on a stock trading at $150, and you own the $100 calls.  At expiration, these have a value of $50.  But let's say, you don't have any money in your account, to take ownership of the underlying security (you have to come up with the additional $100 per share you are missing).  In that case, need to call  your broker and see how they handle it, and it will depend on the type of account you have (e.g. margin or not, IRA, etc).  Generally speaking though, the ""margin department"" makes these decisions, and they look through folks that have options on things that have value, and are expiring, and whether they have the funds in their account to absorb the security they are going to need to own.  Exchange-wise, options that have value at expiration, are exercised.  But what if the person who has the option, doesn't have the funds to own the whole stock? Well, ideally on Monday they'll buy all the shares with the options you have at the current price, and immediately liquidate the amount you can't afford to own, but they don't have to.  I'm mentioning this detail so that it helps you see what's going or needs to go on with exchanges and brokerages and individuals, so you have a broader picture." A stock market is just that, a market place where buyers and sellers come together to buy and sell shares in companies listed on that stock market. There is no global stock price, the price relates to the last price a stock was traded at on a particular stock market. However, a company can be listed on more than one stock exchange. For example, some Australian companies are listed both on the Australian Stock Exchange (ASX) and the NYSE, and they usually trade at different prices on the different exchanges. Also, there is no formula to determine a stock price. In your example where C wants to buy at 110 and B wants to sell at 120, there will be no sale until one or both of them decides to change their bid or offer to match the opposite, or until new buyers and/or sellers come into the market closing the gap between the buy and sell prices and creating more liquidity. It is all to do with supply and demand and peoples' emotions. I just finished a high frequency trading project. Individuals can do it, but you need a lot of capital. You can get a managed server in Times Square for $1500/month, giving you access to 90% of the US exchanges that matter, their data farms are within 3 milliseconds of distance (latency). You can also get more servers in the same building as the exchanges, if you know where to look ;) thats all I can divulge good luck "Why are there so many stock exchanges in the world?  The simple answer is that there is a lot of money to be made by charging fees to facilitate the trading of securities, but there are other factors at play here relating to new technologies. Trading volumes have increased rapidly in recent years.  According to this ITG data, in 1997, 6.5 billion shares were traded on US exchanges.  By 2015 this number had increased to 40.8 billion shares.  There are a number of reasons for this rapid increase in volumes.  Most significant would be the introduction of new technologies that allow for high volume, high frequency trading. This increase in activity has be accompanied by an increase in the number of stock exchanges.  As CQM points out in his answer, there has been considerable consolidation in the ownership of ""legacy"" exchanges.  For example, the NYSE merged with EuroNext in 2007, and the combined group is now owned by the Intercontinental Exchange, which also owns numerous smaller stock exchanges as well as a number of derivative/commodities exchanges. However, this consolidation in ownership has been more than matched by the creation of many ""virtual"" exchanges.   In North America these virtual exchanges are called ""Alternative Trading Systems"".  In Europe, they are called ""Multilateral Trading Facilities"".   These new virtual exchanges, sometimes referred to as ""dark pools"", have begun to significantly eat away at the volumes of the legacy exchanges.  If you look at the ITG data (linked above), you will see that the total volume of shares traded on legacy exchanges actually peaked in 2008, and has since then has decreased.  This coincides roughly with the appearance of the virtual exchanges and the new high frequency trading methods.  According to this paper from the SEC site, dated 2013, Alternative Trading Systems accounted for 11.3% of total volumes in 2012.  This will have increased rapidly in the years since 2012.  It is this loss of business that has prompted the consolidation in the ownership of the legacy exchanges. These new exchange are ""conceptually the same"" as the legacy exchanges and must play by the same regulatory rules." Some brokerages will let you withdraw/deposit in multiple jurisdictions. e.g. I used to use Interactive Brokers. I could deposit/withdraw to US and UK bank accounts, in the appropriate currencies. It helps to have a brokerage that provides good rates on forex exchange also, and they were very good on the bid/ask spread. It was possible to get interbank rates plus a very low commission. "If I buy the one from NSY, is it the ""real"" Sinopec? No - you are buying an American Depository Receipt. Essentially some American bank or other entity holds a bunch of Sinopec stock and issues certificates to the American exchange that American investors can trade.  This insulates the American investors from the cost of international transactions.   The price of these ADRs should mimic the price of the underlying stock (including changes the currency exchange rate) otherwise an arbitrage opportunity would exist.  Other than that, the main difference between holding the ADR and the actual stock is that ADRs do not have voting rights. So if that is not important to you then for all intents and purposes trading the ADR would be the same as trading the underlying stock."