John Eric Ensign (born March 25, 1958) is the junior United States Senator from Nevada, serving since January 2001. He is a member of the Republican Party and the former chairman of the Senate Republican Policy Committee.

Ensign was born in Roseville, California, to Sharon Lee Cipriani and a father whose surname was Mueller; his maternal grandfather was of Italian descent. Ensign claims to be one eighth (1/8th) Filipino American. Ensign's family moved to Nevada when he was a child. His mother remarried Michael S. Ensign, a gaming industry executive who subsequently became chairman of the board of directors of Mandalay Bay, and who adopted John.

Ensign went to UNLV, becoming a member of the Sigma Chi fraternity, Oregon State University, and Colorado State University, becoming a veterinarian in 1985. He then became a successful businessman, opening a 24-hour animal hospital in Las Vegas. He owned two animal hospitals before entering politics.