Does an index have a currency?
From Wikipedia -  To calculate the value of the S&P 500 Index, the sum of the adjusted   market capitalization of all 500 stocks is divided by a factor,   usually referred to as the Divisor. For example, if the total adjusted   market cap of the 500 component stocks is US$13 trillion and the   Divisor is set at 8.933 billion, then the S&P 500 Index value would be   1,455.28. From a strictly mathematical perspective, the divisor is not canceling out the units, and the S&P index is dollar denominated even though it's never quoted that way. A case in point is that the S&P is often said to have a P/E, and especially an E, the earnings attributed to one 'unit' of S&P. And if you buy a mutual fund sporting a low expense ratio, you can invest exactly that much money (the current S&P index value) and see the dividends accrue to your account, less the fee. "There's no need for an index to have a currency as its purpose is not to act as an asset but rather to signal investors about the performance of a collection of stocks. An index can be price-weighted, meaning that its value equals the (arithmetic) average of the prices of each stock in the index. With no stock splits, the return on this index is the same as the return on a portfolio composed of one share of each stock. If there is a stock split, however instead of dividing by the number of stocks, as you normally would when taking the arithmetic average, you divide it by the number that will make the value of the index pre-stock-split (arithmetic average) equal to the value post stock split. Then use that dividing number for all periods until a new stock split occurs.  An index can be value-weighted, meaning that its changes in value track the percentage changes in total market capitalization of the stocks in the index. Price weighted indexes ignore for ""firm size"" and percentage changes in price weighted indexes are not robust to stock-splits. Value weighted indexes take ""firm size"" into account and are robust to stock-splits. DJIA is price-weighted. S&P 500 is value-weighted." "In practice, most (maybe all) stock indices are constructed by taking a weighted average of stock prices denominated in a single currency, and so the index implicitly does have that currency - as you suggest, US dollars for the S&P 500. In principle you can buy one ""unit"" of the S&P 500 for $2,132.98 or whatever by buying an appropriate quantity of each of its constituent stocks. Also, in a more realistic scenario where you buy an index via a tracker fund, you would typically need to buy using the underlying currency of the index and your returns will be relative to that currency - if the index goes up by 10%, your original investment in dollars is up by 10%." More importantly, index funds are denominated in specific currencies. You can't buy or sell an index, so it can be dimensionless. Anything you actually do to track the index involves real amounts of real money.
"It's very hard to measure the worth of an abstract concept like money, particularly over long periods of time. In the modern era we have things like the Consumer Price Index (CPI) in the United States, where the Bureau of Labor Statistics literally sends ""shoppers"" out to find prices of things and surveys people to find out what they buy. This results in a variety of ""indexes"" which variously get reported by media outlets as ""inflation"" (or ""deflation"" if the change in value goes the other way). There are also other measurements available like the MIT Billion Prices Project which attempt to make their own reading of the ""worth"" of currencies. Those kinds of things are about the only ways to measure a currency's change in ""value to itself"" because a currency is basically only worth what one can buy with it. While it isn't ""all the world's currencies combined"", there is a concept of the International Monetary Fund's ""Special Drawing Rights (SDR)"", which is a basket of five currencies used by world central banks to help ""back"" each other's currencies, and is (very) occasionally used as a unit of currency for international contracts. One might be able to compare the price of one currency to that of the SDR, or even to any other weighted average of world currencies that one wanted, but I don't think it's done nearly as often as comparing currencies to the basket of goods one can buy to find ""inflation"". Even though one might think what would be important to measure would be overall Money Supply Inflation, much more often people care more about measuring Price Inflation. (Occasionally people worry about Wage Inflation, but generally that's considered a result of high Price Inflation.) In order to try to keep this on topic as a ""personal finance"" thing rather than an ""economics"" thing, I guess the question is: Why do you want to know? If you have some assets in a particular currency, you probably care most about what you'll be able to buy with them in the future when you want or need to spend them. In that sense, it's inflation that you're likely caring about the most. If you're trying to figure out which currency to keep your assets in, it largely depends on what currency your future expenses are likely to be in, though I can imagine that one might want to move out of a particular currency if there's a lot of political instability that you're expecting to lead to high inflation in a currency for a time." The Federal Reserve Bank publishes exchange rate data in their H.10 release. It is daily, not minute by minute. The Fed says this about their data: About the Release The H.10 weekly release contains daily rates of   exchange of major currencies against the U.S. dollar. The data are   noon buying rates in New York for cable transfers payable in the   listed currencies. The rates have been certified by the Federal   Reserve Bank of New York for customs purposes as required by section   522 of the amended Tariff Act of 1930. The historical EURUSD rates for the value of 1 EURO in US$ are at: http://www.federalreserve.gov/releases/h10/hist/dat00_eu.htm If you need to know USDEUR the value of 1 US$ in EUROS use division 1.0/EURUSD. "For the S&P and many other indices (but not the DJIA) the index ""price"" is just a unitless number that is the result of a complicated formula.  It's not a dollar value.  So when you divide said number by the earnings/share of the sector, you're again getting just a unitless number that is incomparable to standard P-E ratios. In fact, now that I think about, it kinda makes sense that each sector would have a similar value for the number that you're computing, since each sector's index formula is presumably written to make all the index ""price""s look similar to consumers." If I buy VUSA from one exchange, can I sell it in a different exchange, assuming my brokerage account lets me trade in both exchanges? Or is it somehow tied to the exchange I bought it from? This doesn't happen for all securities and between all stock exchanges. So that is dependent on broker and country. I checked for VUSA with Selftrade. They categorically refused allowing me to trade in VUSA in different exchanges. I can only buy and sell in same currency only, albeit sell(buy) in the same exchange where I buy(sell) from. Should be the same behaviour for all brokers for us mere mortals, if you are a bank or a millionaire than that might be a different question.  The VUSA you quote is quoted in GBP in LSE and in EUR in AEX, and the ETF has been created by an Irish entity and has an Irish ISIN.  As Chris mentioned below, happens between US and Canadian exchanges, but not sure it happens across all exchanges. You cannot deal in inter-listed stocks in LSE and NYSE. Since it's the same asset, its value should not vary across exchanges once you compensate for exchange rates, right? Yes, else it opens up itself for arbitrage (profit without any risk) which everybody wants. So even if any such instance occurs, either people will exploit it to make the arbitrage profit zero (security reflects the equilibrium price) or the profit from such transaction is so less, compared with the effort involved, that people will tend to ignore it. Anyways arbitrage profit is very difficult to garner nowadays, considering the super computers at work in the market who exploit these discrepancies, the moment they see them and bring the security right to the zero arbitrage profit point. If there's no currency risk because of #2, what other factors should I consider when choosing an exchange to trade in? Liquidity? Something else? Time difference, by the time you wake up to trade in Japan, the Japanese markets would have closed. Tax implications across multiple continents. Law of the land, providing protection to investors. Finding a broker dealing in markets you want to explore or dealing with multiple brokers. Regulatory headaches. If I understand what you're asking, I think you're looking at the relationship wrong.  Yes, when one currency has a higher interest rate relative to another, it's value should, theoretically, appreciate.  For example, if the USD interest rate is 10% and the EUR is 5%, the USD should appreciate in value against the EUR.  However, the parity relationship tells you the price at which an investor would be indifferent to the difference in interest rates.  So using the formula for interest rate parity:  (1+r(USD))/(1+r(EUR)) = F/S   and plugging in the interest rates from above and a spot rate of $1.5/EUR:  (1.1)/(1.05) = F/(1.5)  The 1 year forward rate would have to be $1.5714/EUR in order for the investor to be INDIFFERENT between holding USD or EUR.  All this assuming interest rate parity holds.  I'm not big on Econ but this is how I understood it when studying for the CFA exam the past few months.  So please, someone correct me if I'm wrong. A target date fund is NOT a world market index. There is no requirement that it be weighted based on the weights of the various world stock markets. If anything, historically (since the invention of target date funds), a 2:1 ratio is actually pretty low. 6:1 is, or was, probably more common. Just a token amount to non-US investments. You can trade VXX, but VIX is only an index.   http://www.marketwatch.com/investing/stock/VXX?CountryCode=US What you want is the average change in rate of the Australian Dollar against multiple other currencies, to even out the effect of moves in a single other currency. People often look at the trade-weighted exchange rate to get an idea of this, as it allows you to look at the currencies that are most relevant, rather than every tiny other currency having an equal weight. "Unless you are buying a significant value of your goods in USD then the relative strength of USD versus your local currency will have little to no effect on what the value of your investments is worth to you. In fact only (de|in)flation will effect your purchasing power. If your investments are in your local currency and your future expenses (usage of the returns on the investments) will be in your local currency FX has no effect. To answer your question, however, since all investments involve flows of money there can be no investment (other than perhaps gold which is really a form of currency) that isn't bound to at least one currency. In general investments are expected to be valued against the investor's home currency (I tend to call it ""fund currency"" as I work with hedge funds) as the return on the investment will be paid out in the fund currency and returns will be compared on the same basis. If investments are to be made internationally then it is necessary to reduce, or ""hedge"" the exchange rate risk. This is normally done using FX swaps or futures that allow an exchange rate in the future to be locked in today. Far from being unbound from FX moves these derivatives are closely bound to any moves but crucially are bound in the opposite direction to the hoped for FX move. an example of this would be if I'm investing 100GBP (my local currency) in a US company XYZ corp which I expect to do well. Suppose I get 200USD for my 100GBP and so buy 1 * 200USD shares in XYZ. No matter what happens to XYZ stock any move in GBP/USD will affect my P&L so I buy a future that allows me to exchange 200USD for 100GBP in 6 month's time. If GBP rises I can sell the future and make money on both the higher exchange rate and the increase in XYZ corp. If GBP falls I can keep the future until maturity and exchange the 200USD from XYZ corp for 100GBP so I only take the foreign exchange hit on any profits. If I expect my profits to be 10USD I can even buy futures such that I can lock in the exchange rate for 110USD in 6 months so that I will lose even less of my profit from the exchange rate move." Depending on what currency the price is quoted in and is originally sold, currency fluctuation can also carry over onto the price in your currency. An example for that would be bitcoin prices which sometimes show heavy ups and downs in one currency, but seem totally stable in another and can be tracked back to changed exchange rates between currencies. Also like others have said, prices on stocks are not actually fixed. You can offer to buy or sell at any price. Only if 2 people want to buy or sell for the same price there will actually be a transaction. No. The long-term valuation of currencies has to do with Purchasing Power Parity.  The long-term valuation of stocks has to do with revenues, expenses, market sizes, growth rates, and interest rates. In the short term, currency and stock prices change for many reasons, including interest rate changes, demand for goods and services, asset price changes, political fears, and momentum investing.  In any given time window, a currency or stock might be: The Relative Strength Index tries to say whether a currency or stock has recently been rising or falling; it does not inherently say anything about whether the current value is high or low. See the FX section of the quantitative finance SE data wiki. "Quicken for Mac will track stocks and mutual funds and allows you to set the ""home"" currency." Gold is traded on the London stock exchange (LSE) and the New York stock exchange (NYSE) under various separate asset tickers, mainly denominated in sterling and US dollars respectively.  These stocks will reflect FX changes very quickly.  If you sold LSE gold and foreign exchanged your sterling to dollars to buy NYSE gold you would almost certainly lose on the spreads upon selling, FX'ing and re-buying. In short, the same asset doesn't exist in multiple currencies.  It may have the same International Securities Identification Number (ISIN), but it can trade with different Stock Exchange Daily Official List (SEDOL) identifiers, reflecting different currencies and/or exchanges, each carrying a different price at any one time. "would constantly fluctuate and provide an indication of how well the market is doing. The index is there to tell if you made profit or loss by investing in the market.  Using a pure total market cap will only tell you ""Did IPO activity exceed bankruptcy and privatization activity""."