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How to change a large quantity of U.S. dollars into Euros?
The right answer to this question really depends on the size of the transfer.  For larger transfers ($10k and up) the exchange rate is the dominant factor, and you will get the best rates from Interactive Brokers (IB) as noted by Paul above, or OANDA (listed by user6714). Under $10k, CurrencyFair is probably your best bet; while the rates are not quite as good as IB or OANDA, they are much better than the banks, and the transaction fees are less.  If you don't need to exchange the currency immediately, you can put in your own bids and potentially get better rates from other CurrencyFair users. Below $1000, XE Trade (also listed by user6714) has exchange rates that are almost as good, but also offers EFT transfers in and out, which will save you wire transfer fees from your bank to send or receive money to/from your currency broker.  The bank wire transfer fees in the US can be $10-$30 (outgoing wires on the higher end) so for smaller transfers this is a significant consideration you need to look into; if you are receiving money in US, ING Direct and many brokerage accounts don't charge for incoming wires - but unless you have a commercial bank account with high balances, expect to spend $10-$20 minimum for outgoing.  European wire transfer fees are minimal or zero in most cases, making CurrencyFair more appealing if the money stays in Europe. Below $100, it's rarely worth the effort to use any of the above services; use PayPal or MoneyBookers, whatever is easiest. Update:  As of December 2013, CurrencyFair is temporarily suspending operations for US residents: Following our initial assessment of regulatory changes in the United States, including changes arising from the Dodd-Frank Act, CurrencyFair will temporarily withdraw services for US residents while we consider these requirements and how they impact our business model.  This was a difficult and very regretful decision but we are confident we will be able to resume services in the future. The exact date of re-activation has not yet been determined and may take some time. We appreciate your patience and will continue communicating our status and expected return.