(CNN) -- It's the annual festival of beer known the world over, and this year, Germany's Oktoberfest turns 200.
People are filling the beer tents and filling their beer mugs on Munich's Theresienwiese, where the festival began two centuries ago as a celebration of the marriage of Crown Prince Ludwig to Princess Therese of Saxony-Hildburghausen, for whom the street is now named.
The royal couple invited the citizens of Munich to attend the festivities, and the party was repeated annually after that.
Today, Oktoberfest is the largest festival in the world, with six million visitors, according to Susanne Muhlbauer, press officer for Munich Tourist Office.
She told CNN: "Part of the fun nowadays is that you actually do dress up in traditional costume.
"When I was a teenager you just wore jeans. It's only over the last 20 years that young people won't go to the festival without wearing traditional lederhosen."
And it's not just the Germans who are dressing up. According to Muhlbauer, over 9,000 people from clubs or "trachtenvereins" across Europe are taking part in this year's festival.
She explained: "It's not just a Bavarian celebration; people come from all over the Alpine region, including guests from Italy, Austria, Poland and Switzerland.
Part of the fun nowadays is that you actually do dress up in traditional costume.
--Susanne Muhlbauer, press officer for Munich Tourist Office
"They all come together to show their traditional costumes, which vary from the length of the lederhosen to the type of feathers in their hat."
But of course beer is the most important part of Oktoberfest, and organizers say around six million liters will be consumed this year. Six different types of the "liquid gold" are available in the tents.
According to Muhlbauer, there is good reason why so much alcohol is consumed.
She told CNN: "What is special about Oktoberfest is that you have to drink beer from a one liter stein. It's a lot of beer and you have to drink it fairly quickly otherwise it goes stale!"
Munich and Bavaria pride themselves on their quality of beer, unashamedly calling it the best in the world. They cite Bavarian Purity Requirements that date to Duke William IV in 1516, which allow only water, hops, and barley to be used in the brewing process.
This year's Oktoberfest runs from September 18 to October 4. Beer is sold in the tents from 10 a.m. to 10:30 p.m. on weekdays and from 9 a.m. to 10:30 p.m. on weekends.
Although Oktoberfest began 200 years ago, this year's festival is only the 177th, since it wasn't held during the two World Wars and during a cholera outbreak, organizers say.
