Berlin is a "Stadtstaat", or "city state". It is both the national capital and one of the sixteen federal states of Germany. The city and state parliament is the House of Representatives (Abgeordnetenhaus), which has 141 seats. Berlin's executive body is the Senate of Berlin which consists of the Mayor and up to eight senators. The city Mayor is simultaneously the prime minister of the federal state. Public elections for the House of Representatives occur every five years.
Since the last elections in 2001 the house has had representatives from the SPD, CDU, Linkspartei, Bündnis 90/Die Grünen, and FDP parties. The Mayor is currently Klaus Wowereit of the SPD.
Politicians from each of these parties, including current Mayor Wowereit, are out campaigning this week. Their campaign posters are to be seen all over the city. Berlin is renowned for having high levels of graffiti, so it's no surprise that the street artists have been joining the election fever.
A large collection of election graffiti can be seen on the flickr pool: Berliner Wahlplakate 2006
Photos included here by: svenwerk, squirm, and akimowitsch.