Thomas Zeuthen Kahlenberg (Danish pronunciation: [ˈkʰɑˀln̩ˌpɛɐ̯ˀ]; born 20 March 1983) is a Danish former professional footballer who played as an attacking midfielder. He started his career with Brøndby IF, winning two Danish Superliga championships, and played abroad at French club Auxerre and German club VfL Wolfsburg. He has played 46 games and scored five goals for the Denmark national team, and represented Denmark at the 2004 European Championship, 2010 FIFA World Cup and 2012 European Championship. He was named 2004 Danish under-21 Player of the Year.

Born in Hvidovre, Denmark, Kahlenberg was fifteen years old when he moved from lower-league club Hvidovre IF to Brøndby. Kahlenberg progressed through the ranks at the club's youth system and said that he learned a lot from development to "behaving as a professional footballer". In April 2002, Kahlenberg signed his first professional contract with Brøndby. After the club's youth team coach Tom Køhlert was promoted to head coach, he made his Superliga debut against arch-rivals, København on 12 May 2002, in a 1–1 draw, at the penultimate match of the 2001–02 season and helped Brøndby secure the 2001–02 Danish championship on goal difference. Kahlenberg went on to make two appearances in all competitions.

At the start of the 2002–03 season, Kahlenberg played in the central midfield for Brøndby, where he set up the attacks with his great technique and view for the game. Kahlenberg made his UEFA Champions League debut, coming against Dinamo Tirana in the first leg of the tournament second round, starting a match and played 67 minutes before being substituted, in a 1–0 win. In the return leg, Kahlenberg started the whole game, as he helped the club win 4–0 to progress to the next round. Kahlenberg made an interview over his frustration to score his first goal despite making good chances. But on 10 November 2002 he scored his first goal for Brøndby, in a 1–1 draw against Esbjerg fB. His performance led him to sign a contract extension, keeping him until 2006. Two weeks later on 23 November 2002, Kahlenberg scored his second goal for the club, in a 7–1 win against Farum BK. A month later, he was named Talent of the Year by the Players' Association and Ekstrabladet. His performance attracted interests from European clubs, leading his agent stating Kahlenberg is worth 5 million kroner. He later scored two more goals later in the 2002–03 season, coming against FC Midtjylland and Odense BK. However, Brøndby failed to defend the league title after they ended up finishing second place in the league. Despite this, Kahlenberg helped the club reach the Danish Cup Final after beating AaB 4–1 on aggregate. In the final against FC Midtjylland, he started the whole game, as Brøndby won 3–0 to win the tournament. Despite suffering injuries during the 2002–03 season, he ended the season, making forty–three appearances and scoring four times in all competitions.

At the start of the 2003–04 season, Kahlenberg continued to establish himself in the starting eleven, playing in the central midfield for Brøndby. However, in a match against Viborg on 17 August 2003, he was sent–off for a second bookable offence, in a 2–2 draw and served a one match suspension as a result. Amid to serving a one match suspension, Kahlenberg played in both legs of the UEFA Cup Qualification Round, as he helped the club win 5–0 on aggregate against Dinamo Minsk. Kahlenberg returned to the starting line–up against FC Nordsjælland on 31 August 2003 and set up Brøndby's only goal of the game, in a 1–0 win. This was followed up by scoring his first goal of the season, in a 3–0 win against Akademisk Boldklub. Six days later, on 20 September 2003, he scored his second goal of the season, in a 1–0 win against Nordsjælland. It was announced on 3 October 2003 that Kahlenberg signed a contract with Brøndby, keeping him until 2008. This was followed up by scoring in the next two matches against Esbjerg fB (brace) and AGF. He then scored two more goals by the end of the year. Kahlenberg also played an important role in the UEFA Cup matches when he helped the club beat Viktoria Žižkov and Schalke 04. A month later, Kahlenberg, once again, was named Talent of the Year by the Players' Association and Ekstrabladet. Despite signing a contract with Brøndby, his performance continued to attract interests from European clubs, mostly from Germany, but he ended up staying at the club. Kahlenberg then scored two separate in two separate matches; the first one came between 18 April 2004 and 24 April 2004 against AaB and Viborg respectively; and the second one came between 16 May 2004 and 23 May 2004 against FC Midtjylland and BK Frem. However, Brøndby, once again, finished second in the league. Despite facing setbacks during the 2003–04 season, he went on to make forty–two appearances and scoring twelve times in all competitions, making him the club's top scorer.

In the 2004–05 season, Kahlenberg was moved out as left midfielder, following the sale of Swedish international left winger Mattias Jonson. He started the season well by setting up two goals in the first two league matches of the season. However, Kahlenberg was sent–off for a second bookable offence against FK Ventspils in the second leg of the UEFA Cup second round qualification, as the club were eliminated from the tournament. On 25 September 2004 Kahlenberg scored twice for the club, as they won 4–1 against Herfølge Boldklub. He later scored three more goals, including a brace against AGF on 21 November 2004. Cutting into the field from his wide position, Kahlenberg scored eight more goals, including a two braces against København and Herfølge Boldklub. Kahlenberg managed to become Brøndby's 2004–05 league top goal scorer with 13 goals. He also helped the club win the Double, both the league and Danish Cup. At the end of the 2004–05 season, Kahlenberg went on to make forty appearances and scoring thirteen times in all competitions.

By the time he departed the club, Kahlenberg played a combined total of 130 games for Brøndby IF, including 97 games and 28 goals in the Danish Superliga championship. Since leaving Brøndby, the club would suffered a set-back when they find themselves in relegation threatening and economic problems. Kahlenberg expressed sadness and sympathy of the club of what they been through.

It was announced on 13 July 2005 that the French club Auxerre signed Kahlenberg on a four–year contract with the club for a fee of £2.5 million (30 million. kr). After the move, Kahlenberg says he is looking forward to play in Ligue 1.

Kahlenberg made his debut for Auxerre debut, starting the whole game, in a 4–1 loss against Lyon in the Trophée des Champions. In a follow–up match, he made his league debut for the club, starting the whole game, in a 0–0 draw against Strasbourg in the opening game of the season. Since joining Auxerre, Kahlenberg quickly established himself in the starting eleven, playing in the midfield position. On 24 September 2005 he scored his first goal for the club, in a 3–0 win against Sochaux. Kahlenberg then scored his second goal of the season, as well as, setting up one of Auxerre's goals, in a 2–1 win against AS Monaco on 5 January 2006. Following the match, he was named Team of the Week by L’Equipe. This was followed up by scoring against Olympique Noisy-le-Sec in the first round of the Coupe de France. Kahlenberg scored his fourth goal of the season, in a 2–0 win against Rennes on 28 January 2006. He later scored five more goals later in the 2005–06 season, including two consecutive goals in two separate matches. Kahlenberg also made the most assists of all players in the 2005–06 championship season. In his first season at the club, he went on to make forty–three appearances and scoring nine times in all competitions.