At Restaurants: 10–15 percent to the waiter or bartender—just add it to the bill.

At Hotels: One to three euros per bag for the porter; five euros per night for the housekeeper; 20 euros for a helpful concierge.

Dollars Accepted? Yes, but euros are recommended.

P.S. Despite its reputation for precision, Germany has no hang-ups about generous tipping.

Source : CNTraveler.com