Ballspielverein Borussia 09 e. V. Dortmund, often known simply as Borussia Dortmund (German pronunciation: [boˈʁʊsi̯a ˈdɔɐ̯tmʊnt] ) or by its initialism BVB (pronounced [beːfaʊ̯ˈbeː] ), 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.

Founded in 1909 by eighteen football players from Dortmund, they are nicknamed Die Schwarzgelben (The Black and Yellow), for the colours used in the club's crest. They hold a long-standing rivalry with Ruhr neighbours Schalke 04, against whom they contest the Revierderby. They also contest Der Klassiker with Bayern Munich. Dortmund is the second largest sports club by membership in Germany, with about 218,000 members, making Borussia Dortmund the fifth largest sports club by membership in the world. The club also has a women's handball team. Since 1974, Dortmund have played their home games at the Westfalenstadion; the stadium is the largest in Germany, the Yellow Wall, a standing terrace in the South Stand, is the largest of its kind in Europe, and Dortmund has the highest average attendance of any association football club in the world.

Dortmund is the second most decorated German football team, domestically, they have eight league championships, five DFB-Pokals, and six DFL-Supercups. Internationally, they won the UEFA Champions League in 1997, the European Cup Winners' Cup in 1966, and the Intercontinental Cup in 1997. In addition, they were runners-up in the Champions League in 2013 and 2024 and UEFA Europa League (formerly the UEFA Cup) in 1993 and 2002.

Under the directorship of Michael Zorc in the 2010s, Dortmund cultivated a reputation for spotting and developing young talent, and have remained focused on developing a youth system. As of 2024, Dortmund had the second most revenue across football clubs in Germany, and the 12th most revenue across all football teams in the world, per Deloitte's Football Money League.