Bart Claessen (Dutch pronunciation: [ˈbɑrt ˈklaː.sə(n)]) (born January 22, 1980, Asten, Netherlands) is a Dutch trance music DJ. He is best known for his dance tracks, "On the Move" (2001) and "Infected" (2002) (both as Barthezz), which reached Number 18 and 25 in the UK Singles Chart respectively.

He has released a number of tracks under his own name, most notably "First Light" (2007) and "Madness" (2008).