Mark Emery Udall (born July 18, 1950) is the senior United States Senator from Colorado and a member of the Democratic Party. From 1999 to 2009, Udall served as a five-term member of the United States House of Representatives, representing Colorado's 2nd congressional district. He also served a term in the Colorado House of Representatives.

Udall won the 2008 United States Senate election, defeating Republican challenger Bob Schaffer. He became Colorado's senior Senator just 17 days into his first term, as Ken Salazar resigned his seat to become United States Secretary of the Interior.

Mark was born in Tucson, Arizona and is the son of Morris "Mo" Udall, a former congressman from Arizona and candidate for the Democratic Presidential nomination in 1976. He is a first cousin of Senator Tom Udall of New Mexico and a double second cousin of former Senator Gordon Smith of Oregon. He is also the nephew of former Interior Secretary Stewart Udall. The Udall family, with its years of service in the public sector, is one of the more well known families in the United States.