Justin Gimelstob, born in Livingston, January 26, 1977, is a tennis coach and former American tennis player.

Tennis player with a good career in doubles, in this specialty he won thirteen titles as well as two Grand Slam titles in mixed doubles, together with Venus Williams.
In singles he never made it past the third round at the Grand Slams, instead reaching a final at the 2006 Hall of Fame Tennis Championships but being defeated by Mark Philippoussis in straight sets.

After his retirement, he pursued a career as a commentator for the Tennis Channel as well as doing courtside interviews at the US Open. He also owns a blog, which he manages for his collaborations with Sports Illustrated.

The tennis world remembers his name in particular for the fact that in the 1st round of the Miami tournament in 2000, he was the first "victim" of the first victory in the ATP circuit of the then unknown great Roger Federer. Currently he is one of the staff members of the American John Isner.