Most Germans still make most of—if not all—their purchases the old-fashioned way: with cash. The use of credit cards in Germany is among the lowest in Europe. That said, you should be able to pay your hotel bill, train tickets, or car rental with a credit card.
But if you’re picking up a snack at a bakery, a little souvenir, or having a cup of coffee, you'll need cash. The same goes for buying tickets on public transportation or paying for a taxi.
Exchange services and banks are plentiful in cities and towns. However keep in mind that you’ll generally get the best exchange rate at a Geldautomat (ATM), not to mention the convenience of 24-hour access. Before starting your trip, check on the fees your bank charges for international ATM transactions. You may find that these are less than the commissions charged at currency exchange booths and banks.