American Depositary Receipts, or ADRs, make it possible for folks in America to easily buy and sell shares of foreign companies that don't normally trade on U.S. exchanges. Without them, if you wanted to buy stock in Volkswagen AG, you'd have to convert your dollars into euro and then somehow buy shares on the German DAX stock exchange. Through ADRs, shares of Volkswagen are held by an American financial institution overseas, and you can trade shares with U.S. dollars. ADR holders are entitled to dividends and capital gains, but they have no voting rights.
Some other well-known names that trade as ADRs in the U.S. include Allied Domecq PLC (NYSE:AED), Bayer AG (NYSE:BAY), BASF AG (NYSE:BF), Benetton (NYSE:BNG), GlaxoSmithKline PLC (NYSE:GSK), Nestle, Nokia (NYSE:NOK), and Sony (NYSE:SNE).