Mayor Dieter Reiter inserted the tap into the first keg Saturday with two blows of his hammer and the cry of "O'zapft is" - "It's tapped".
About 6 million visitors are expected to come to Munich for the 184th Oktoberfest, which runs through October 3.
The prices for a big mug of beer have gone up again and visitors have to pay 10.95 euros (about $13) per glass - 25 cents more than last year.
Revelers also face increased security precautions because of possible attacks. Huge flower pots block the entrances to the fest's lawn, more video cameras are installed and a new loudspeaker system has been activated to guide visitors off the festival's grounds if necessary
Oktoberfest is the world's largest beer festival and travelling funfair. It is held annually in Munich, Bavaria, Germany. The folk festival lasts about 16 to 18 days from mid or late September to the first weekend in October since its initiation in 1810.
People attend the festival from all around the world, and it is an important part of Bavarian culture.
