Döner Kebab, or just döner, is undoubtedly the most popular street food in Germany and has become part of the German culinary culture and vocabulary, much like Indian chicken tikka masala has in the UK. The döner was first introduced to the Berliner neighborhoods of Kreuzberg (known as Little Istanbul) and Neukölln in the early 1970s by Turkish immigrants invited to contribute to west Germany's Wirtschaftswunder (economic miracle). It quickly spread to other (west) German urban centers and following German reunification became so popular, you'll find a döner stand in every single German town today, even in Bavaria.
According to the European Association of Turkish Döner Producers, more than 100,000 tons of döner meat is annually consumed in Germany. This translates into two million döners sold and eaten every single day, surpassing all other German fast food dishes including the currywurst. In Berlin alone there are over 1,300 döner stands.
The döner consists of a lightly toasted round flatbread (similar to pita) filled with chopped roasted meat and garnished with mixed red and white cabbage, tomatoes, onions, cucumbers, pickled peppers and feta. A choice of sauces typically includes garlic sauce, herb sauce, or just plain yogurt. The döner meat—made of compressed layers lamb, calf, beef, and sometimes turkey—is subjected to a slow rotating vertical spit roast.
When you order a döner, the meat should be sliced directly from the spit, chopped and placed right into your flatbread.
Some years ago the döner's reputation took severe hits (and it's still recovering) after it was discovered that the producers were supplying decayed meat to thousands of döner stands. The public was, rightfully so, enraged. The Turkish community suspected a conspiracy from the established fast food industry to bring down the increasingly popular döner. Germans don't take such matters lightly and the scandal prompted strict government regulations on what goes into a döner. The scandal also revealed poor standards of hygiene at many stands.
Use common sense: take a close look at the meat and the overall cleanliness of the shop and vendors. If it doesn't look good, leave. The next döner stand is just around the corner, if not nextdoor. In my experience the majority of döner stands in Berlin now operate under sound hygienically standards. The best ones also offer true bazaar ambiance with traditional local music and will serve you a free glass of hot Turkish black tea (Çay) while you wait for your Döner.
I must confess that I seldom eat döner. I prefer schwarma, also offered all over town, the best of course being Habibi's at Winterfeldt market just around the corner from my apartment.