A currency swap (or cross currency swap) is a foreign exchange agreement between two parties to exchange a given amount of one currency for another and, after a specified period of time, to give back the original amounts swapped.
Currency swaps can be negotiated for a variety of maturities up to 30 years. Unlike a back-to-back loan, a currency swap is not considered to be a loan by United States accounting laws and thus it is not reflected on a company's balance sheet. A swap is considered to be a foreign exchange transaction (short leg) plus an obligation to close the swap (far leg) being a forward contract.
Unlike interest rate swaps, currency swaps involve the exchange of the principal amount. Interest payments are not netted (as they are in interest rate swaps) because they are denominated in different currencies.
Currency swaps are often combined with interest rate swaps. For example, one company would seek to swap a cash flow for their fixed rate debt denominated in US dollars for a floating-rate debt denominated in Euro. This is especially common in Europe where companies "shop" for the cheapest debt regardless of its denomination and then seek to exchange it for the debt in desired currency.