Justin Jeremy Gimelstob (born January 26, 1977) is a retired American tennis player. Gimelstob has been a resident of Morristown, New Jersey, and as of 2009 lived in Santa Monica, California.

He was the top-ranked boy in his age group at the ages of 12, 14, 16, and 18. As a pro, he made the final of the Newport Tournament in singles and has 15 doubles championships to his name, including the 1998 Australian Open and 1998 French Open mixed doubles titles with Venus Williams. He was twice a member of the U.S. Davis Cup team.

In singles matches, he defeated Andre Agassi, Petr Korda, Àlex Corretja, Pat Rafter, and Gustavo Kuerten. His career singles record is 107–172. His highest career singles ranking was No. 63 in 1999, and his highest career doubles ranking was No. 18 in 2000.

Gimelstob most recently coached American John Isner.