Berlin has two Airports; Tegel, about 10km from the centre of the city, and Shoenefeld, about 20km to the south-east of the city. Tegel is the main international airport and services most of the large carriers such as the national airline Lufthansa, Delta Airways, British Airways, Continental Airways, Emirates and KLM. There are plenty of public transportation options to get to the city from Tegel; the S-Bahn, U-Bahn and the buses all have dedicated lines. This is probably the easiest method as well, but for extra convenience you can take a taxi, which will cost around €30 to the city.
Shoenefeld was the international airport of East Germany when the country was split. It is now a thriving hub and services smaller carriers such as Aer Lingus, EgyptAir, RyanAir, and Iceland Express. It is also accessible by the trains, buses and S-Bahn. It is about to be expanded and revamped to make it the Berlin-Brandenburg International Airport while Tegel is scheduled to be shut down.