David Hendrik Jansen (born August 21, 1979) is an American mixed martial artist. He has fought for the WEC and Bellator.
MMA career 
World Extreme Cagefighting 
Jansen defeated Richard Crunkilton via unanimous decision in his WEC debut at WEC 43 on October 10, 2009.
Jansen suffered his first professional loss against Kamal Shalorus on January 10, 2010 at WEC 46.
Jansen next fought Ricardo Lamas on August 18, 2010 at WEC 50. He lost the fight via unanimous decision.
After his consecutive losses in the WEC, Jansen was released from the promotion.
Bellator Fighting Championships 
Jansen made his Bellator debut at Bellator 39, defeating Scott McAfee by first round submission.
Jansen next defeated Ashkan Morvari by rear naked choke in the second round at Bellator 57.
Jansen won his third straight Bellator fight when he defeated Jacob Kirwan via unanimous decision at Bellator 62.
Jansen faced Magomed Saadulaev in the quarter final round of the Bellator Lightweight Tournament on October 19, 2012 at Bellator LXXVII. He won the fight via guillotine choke in the third round. He faced Ricardo Tirloni in the semifinals on November 16, 2012 at Bellator 81. Jansen won via split decision to advance to the finals of the Bellator lightweight tournament.
Jansen was expected to face Marcin Held for the season 7 tournament final at Bellator 84 but Held was not allowed in the Horseshoe casino, in Hammond, Indiana where the event was being held since he was only 20 years old, and therefore the fight has been pushed to sometime during Bellator Fighting Championships: Season Eight.
The bout with Held was rescheduled for March 7, 2013 at Bellator 92. Jansen won the fight via unanimous decision to earn a Lightweight title shot.