Ballspielverein Borussia 09 e. V. Dortmund, often known simply as Borussia Dortmund or by its initialism BVB, 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. The club have won eight league championships, five DFB-Pokals, one UEFA Champions League, one Intercontinental Cup, and one UEFA Cup Winners' Cup. Founded in 1909 by eighteen football players from Dortmund, the football team is part of a large membership-based sports club with more than 189,000 members in 2023, 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, and Dortmund has the highest average attendance of any association football club in the world. Borussia Dortmund's colours are black and yellow, giving the club its nickname die Schwarzgelben. 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. 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.

Westfalenstadion (lit. 'Westphalia stadium') is a football stadium in Dortmund, North Rhine-Westphalia, Germany, which is the home stadium of Borussia Dortmund. Officially called Signal Iduna Park for sponsorship reasons and BVB Stadion Dortmund in UEFA competitions, the name derives from the former Prussian province of Westphalia. It has a league capacity of 81,365 (standing and seated) and an international capacity of 65,829 (seated only). It is Germany's largest stadium, the sixth-largest in Europe, and the third-largest home to a top-flight European club after Camp Nou and Santiago Bernabéu Stadium. It holds the European record for average fan attendance, set in the 2011–12 season with almost 1.37 million spectators over 17 games at an average of 80,588 per game. Sales of annual season tickets amounted to 55,000 in 2015. The 24,454 capacity Südtribüne (South Bank) is the largest terrace for standing spectators in European football. Famous for the intense atmosphere it breeds, the south terrace has been nicknamed Die Gelbe Wand, meaning "The Yellow Wall". The Borusseum, the museum of Borussia Dortmund, is located in the north-east part of the stadium. The stadium hosted matches in the 1974 and 2006 FIFA World Cups. It also hosted the 2001 UEFA Cup final. Various national friendlies and qualification matches for World and European tournaments have been played there, as well as matches in European club competitions.