Theo Janssen (born 27 July 1981) is a Dutch former footballer who played as a midfielder for various clubs in the Netherlands, including Vitesse Arnhem, Twente and Ajax, as well as on loan for Belgian club Genk. He spent 10 years with Vitesse before joining Twente in 2008, where he helped them win the Eredivisie and qualify for the Champions League for the first time in their history. After being named Dutch Footballer of the Year in 2011, he played a season with Ajax, before returning to Vitesse in August 2012.
Janssen began his career at amateur club Vitesse Arnhem 1892 and played from 1995–1996 in the reserves of SBV Vitesse. After breaking through in several youth teams Janssen made his professional debut on 9 December 1998 in the first team against NAC Breda, which Vitesse won 2–0. Janssen came in as substitute in 90th minute to replace Marian Zeman. Janssen played 5 games that season for Vitesse. The next season Janssen made 17 appearances for Vitesse. In the 2000–2001 season Janssen became a starter for Vitesse and made 30 appearances, in which he scored once. In September Janssen broke his shin, he played 10 games total that season, and scored 1 goal.