Why would a central bank or country not want their currency to appreciate against other currencies?
I wrote about the dynamic of why either of a lower or higher exchange rate would be good for economies in Would dropping the value of its currency be good for an economy? A strong currency allows consumers to   import goods cheaply from the rest of   the world.  A weak currency allows   producers to export goods cheaply to   the rest of the world.  People are   both consumers and producers.    Clearly, there have to be trade-offs. Strong or weak mean relative to Purchasing Power Parity (i.e. you can buy more or less of an equivalent good with the same money). Governments worrying about unemployment will try and push their currencies weaker relative to others, no matter the cost.  There will be an inflationary impact (imported inputs cost more as a currency weakens) but a country running a major surplus (like China) can afford to subsidise these costs. It would essentially make goods from other countries more cheaper than goods from US. And it would make imports from these countries to China more expensive.  The below illustration is just with 2 major currencies and is more illustrative to show the effect. It does not actually mean the goods from these countries would be cheaper. 1 GBP = 1.60 USD  1 EUR = 1.40 USD 1 CNY = 0.15 USD Lets say the above are the rates for GBP, EUR, CNY. The cost of a particular goods (assume Pencils) in international market is 2 USD. This means for the cost of manufacturing this should be less than GBP 1.25 in UK, less than 1.43 in Euro Countires, less than 13.33 CNY in China. Only then export would make sense. If the real cost of manufacturing is say 1.4 GBP in UK, 1.5 EUR in Euro countires, clearly they cannot compete and would loose. Now lets say the USD has appreciated by 20% against other currencies. The CNY is at same rate. 1 GBP = 1.28 USD 1 EUR = 1.12 USD 1 CNY = 0.15 USD Now at this rate the cost of manufacturing should be less than GBP 1.56 GBP, less than 1.78 EUR in Euro Countires. In effect this is more than the cost of manufacturing. So in effect the goods from other countires have become cheaper/compatative and goods from China have become expensive. Similarly the imports from these countires to China would be more expensive.
"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." "When you invest in an S&P500 index fund that is priced in USD, the only major risk you bear is the risk associated with the equity that comprises the index, since both the equities and the index fund are priced in USD. The fund in your question, however, is priced in EUR. For a fund like this to match the performance of the S&P500, which is priced in USD, as closely as possible, it needs to hedge against fluctuations in the EUR/USD exchange rate. If the fund simply converted EUR to USD then invested in an S&P500 index fund priced in USD, the EUR-priced fund may fail to match the USD-priced fund because of exchange rate fluctuations. Here is a simple example demonstrating why hedging is necessary. I assumed the current value of the USD-priced S&P500 index fund is 1,600 USD/share. The exchange rate is 1.3 USD/EUR. If you purchase one share of this index using EUR, you would pay 1230.77 EUR/share:  If the S&P500 increases 10% to 1760 USD/share and the exchange rate remains unchanged, the value of the your investment in the EUR fund also increases by 10% (both sides of the equation are multiplied by 1.1):  However, the currency risk comes into play when the EUR/USD exchange rate changes. Take the 10% increase in the price of the USD index occurring in tandem with an appreciation of the EUR to 1.4 USD/EUR:  Although the USD-priced index gained 10%, the appreciation of the EUR means that the EUR value of your investment is almost unchanged from the first equation. For investments priced in EUR that invest in securities priced in USD, the presence of this additional currency risk mandates the use of a hedge if the indexes are going to track. The fund you linked to uses swap contracts, which I discuss in detail below, to hedge against fluctuations in the EUR/USD exchange rate. Since these derivatives aren't free, the cost of the hedge is included in the expenses of the fund and may result in differences between the S&P500 Index and the S&P 500 Euro Hedged Index.  Also, it's important to realize that any time you invest in securities that are priced in a different currency than your own, you take on currency risk whether or not the investments aim to track indexes. This holds true even for securities that trade on an exchange in your local currency, like ADR's or GDR's. I wrote an answer that goes through a simple example in a similar fashion to the one above in that context, so you can read that for more information on currency risk in that context.  There are several ways to investors, be they institutional or individual, can hedge against currency risk. iShares offers an ETF that tracks the S&P500 Euro Hedged Index and uses a over-the-counter currency swap contract called a month forward FX contract to hedge against the associated currency risk. In these contracts, two parties agree to swap some amount of one currency for another amount of another currency, at some time in the future. This allows both parties to effectively lock in an exchange rate for a given time period (a month in the case of the iShares ETF) and therefore protect themselves against exchange rate fluctuations in that period.  There are other forms of currency swaps, equity swaps, etc. that could be used to hedge against currency risk. In general, two parties agree to swap one quantity, like a EUR cash flow, payments of a fixed interest rate, etc. for another quantity, like a USD cash flow, payments based on a floating interest rate, etc. In many cases these are over-the-counter transactions, there isn't necessarily a standardized definition.  For example, if the European manager of a fund that tracks the S&P500 Euro Hedged Index is holding euros and wants to lock in an effective exchange rate of 1.4 USD/EUR (above the current exchange rate), he may find another party that is holding USD and wants to lock in the respective exchange rate of 0.71 EUR/USD. The other party could be an American fund manager that manages a USD-price fund that tracks the FTSE. By swapping USD and EUR, both parties can, at a price, lock in their desired exchange rates.  I want to clear up something else in your question too. It's not correct that the ""S&P 500 is completely unrelated to the Euro."" Far from it. There are many cases in which the EUR/USD exchange rate and the level of the S&P500 index could be related. For example: Troublesome economic news in Europe could cause the euro to depreciate against the dollar as European investors flee to safety, e.g. invest in Treasury bills. However, this economic news could also cause US investors to feel that the global economy won't recover as soon as hoped, which could affect the S&P500.  If the euro appreciated against the dollar, for whatever reason, this could increase profits for US businesses that earn part of their profits in Europe. If a US company earns 1 million EUR and the exchange rate is 1.3 USD/EUR, the company earns 1.3 million USD. If the euro appreciates against the dollar to 1.4 USD/EUR in the next quarter and the company still earns 1 million EUR, they now earn 1.4 million USD. Even without additional sales, the US company earned a higher USD profit, which is reflected on their financial statements and could increase their share price (thus affecting the S&P500). Combining examples 1 and 2, if a US company earns some of its profits in Europe and a recession hits in the EU, two things could happen simultaneously. A) The company's sales decline as European consumers scale back their spending, and B) the euro depreciates against the dollar as European investors sell euros and invest in safer securities denominated in other currencies (USD or not). The company suffers a loss in profits both from decreased sales and the depreciation of the EUR.  There are many more factors that could lead to correlation between the euro and the S&P500, or more generally, the European and American economies. The balance of trade, investor and consumer confidence, exposure of banks in one region to sovereign debt in another, the spread of asset/mortgage-backed securities from US financial firms to European banks, companies, municipalities, etc. all play a role.  One example of this last point comes from this article, which includes an interesting line: Among the victims of America’s subprime crisis are eight municipalities in Norway, which lost a total of $125 million through subprime mortgage-related investments. Long story short, these municipalities had mortgage-backed securities in their investment portfolios that were derived from, far down the line, subprime mortgages on US homes. I don't know the specific cities, but it really demonstrates how interconnected the world's economies are when an American family's payment on their subprime mortgage in, say, Chicago, can end up backing a derivative investment in the investment portfolio of, say, Hammerfest, Norway." If you do not understand the volatility of the fx market, you need to stop trading it, immediately. There are many reasons that fx is riskier than other types of investing, and you bear those risks whether you understand them or not. Below are a number of reasons why fx trading has high levels of risk: 1) FX trades on the relative exchange rate between currencies. That means it is a zero-sum game. Over time, the global fx market cannot 'grow'. If the US economy doubles in size, and the European economy doubles in size, then the exchange rate between the USD and the EUR will be the same as it is today (in an extreme example, all else being equal, yes I know that value of currency /= value of total economy, but the general point stands).  Compare that with the stock market - if the US economy doubles in size, then effectively the value of your stock investments will double in size. That means that stocks, bonds, etc. tied to real world economies generally increase when the global economy increases - it is a positive sum game, where many players can be winners. On the long term, on average, most people earn value, without needing to get into 'timing' of trades. This allows many people to consider long-term equity investing to be lower risk than 'day-trading'. With FX, because the value of a currency is in its relative position compared with another currency, 1 player is a winner, 1 player is a loser. By this token, most fx trading is necessarily short-term 'day-trading', which by itself carries inherent risk. 2) Fx markets are insanely efficient (I will lightly state that this is my opinion, but one that I am not alone in holding firmly). This means that public information about a currency [ie: economic news, political news, etc.] is nearly immediately acted upon by many, many people, so that the revised fx price of that currency will quickly adjust. The more efficient a market is, the harder it is to 'time a trade'. As an example, if you see on a news feed that the head of a central bank authority made an announcement about interest rates in that country [a common driver of fx prices], you have only moments to make a trade before the large institutional investors already factor it into their bid/ask prices. Keep in mind that the large fx players are dealing with millions and billions of dollars; markets can move very quickly because of this. Note that some currencies trade more frequently than others. The main currency 'pairs' are typically between USD and / or other G10 country-currencies [JPY, EUR, etc.]. As you get into currencies of smaller countries, trading of those currencies happens less frequently. This means that there may be some additional time before public information is 'priced in' to the market value of that currency, making that currency 'less efficient'. On the flip side, if something is infrequently traded, pricing can be more volatile, as a few relatively smaller trades can have a big impact on the market.  3) Uncertainty of political news. If you make an fx trade based on what you believe will happen after an expected political event, you are taking risk that the event actually happens. Politics and world events can be very hard to predict, and there is a high element of chance involved [see recent 'expected' election results across the world for evidence of this]. For something like the stock market, a particular industry may get hit every once in a while with unexpected news, but the fx market is inherently tied to politics in a way that may impact exchange rates multiple times a day. 4) Leveraging. It is very common for fx traders to borrow money to invest in fx. This creates additional risk because it amplifies the impact of your (positive or negative) returns. This applies to other investments as well, but I mention it because high degrees of debt leveraging is extremely common in FX. To answer your direct question: There are no single individual traders who spike fx prices - that is the impact you see of a very efficient market, with large value traders, reacting to frequent, surprising news.  I reiterate: If you do not understand the risks associated with fx trade, I recommend that you stop this activity immediately, at least until you understand it better [and I would recommend personally that any amateur investor never get involved in fx at all, regardless of how informed you believe you are]. "Currencies that are pegged or fixed require that foreign currencies are held by the central issuer at a proportional amount. This is analogous to having a portfolio of currencies that the central bank issues shares from - in the form of its own currency. We will continue with this analogy, if the central bank says these ""shares"" are worth $1, but the underlying components of the portfolio are worth $0.80 and decreasing, then it is expensive for the central bank to maintain its peg, and eventually they will have to disregard the peg as people start questioning the central bank's solvency. (People will know the $1 they hold is not really worth what the central bank says it is, because of the price changes people experience in buying goods and services, especially when it comes to imports. Shadow economies will also trade using a currency more reflective of labor, which happens no matter what the government's punishments are for doing so). Swiss National Bank (central bank) did this in early 2015, as it experienced volatility in the Euro which it had previously been trying to keep it's currency pegged to. It became too expensive for it to keep this peg on its own. The central bank can devalue its currency by adjusting the proportions of the reserve, such as selling a lot of foreign currency X, buying more of currency Y. They can and do take losses doing this. (Swiss National Bank is maintaining a large loss) They can also flood their economy with more of their currency, diluting the value of each individual 1 dollar equivalent. This is done by issuing bonds or monetizing goods and services from the private sector in exchange for bonds. People colloquially call this ""printing money"" but it is a misnomer in this day and age where printers are not relevant tools. The good and service goes onto the central bank's balance book, and the company/entity that provided the service now has a bond on its book which can be immediately sold to someone else for cash (another reading is that the bond is as good as cash). The bond didn't previously exist until the central bank said it did, and central banks can infinitely exchange goods and services for bonds. Bond monetization (also called Quantitative Easing) is practiced by the Federal Reserve in the United States, Bank of Japan, European Central Bank and now the Central Bank of the Republic of China" 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. Swaps form backstop to a shit load of int'l trade. Liquidity of currency is a huge factor in being a govt reserve currency, which USD currently has the VAST majority of holdings. This agreement is a shove against USE dominance in trade settlements, which is negative. Also challenges us general capital markets dominance a bit It's because a lot of the QE money is parked in excess reserves at the fed. They pay a high enough interest rate to prevent outflows into the rest of the market. We are seeing huge amounts of price inflation in certain asset classes. Things like cryptocurrency and the stock market. Given the way people act in reality, I think this would lead to people buying ponzi scheme currencies, or preferring the ones with the best advertising budgets or aesthetic look, or otherwise getting constantly scammed.  I certainly don't think people would usually save in the best reputation currencies, and if they did, I figure those currencies would get new management once they became successful, who would sell them out for short term gain and be just as prone to printing their buddies out of bankruptcy as the government.  If even nation states, who have a very strong long term interest in maintaining good currency, play all sorts of shenanigans with it, I see no reason to expect bodies with shorter term interests would do a better job.