This article is from the Europe FAQ, by Yves Bellefeuille email@example.com with help from Martin Rich M.G.Rich@city.ac.uk.
Foreign exchange establishments list a "buy" rate and a "sell" rate for
various currencies. The rates are shown from the establishment's point
of view: if you want to obtain the local currency, look at the "buy"
rate for your own currency, since the establishment is "buying" your
currency and giving you the local currency in exchange. The difference
between the two rates reflects the establishment's profit.
Before changing any money, make sure you know the exchange rate and any
commission or charges.