Ballspielverein Borussia 09 e. V. Dortmund, often known simply as Borussia Dortmund or by its initialism BVB, or just Dortmund by international fans, is a German professional sports club based in Dortmund, North Rhine-Westphalia. It is best known for its men's professional football team, which plays in the Bundesliga, the top tier of the German football league system.