Jason Samuel Christiansen (born September 21, 1969) is a former Major League Baseball left-handed relief pitcher.

Christiansen was born in Omaha, Nebraska and attended Elkhorn High School.

Christiansen gained national attention for his heated rivalry with fellow San Francisco Giants teammate Barry Bonds during the 2005 season.

On December 13, 2007, he was named in the Mitchell Report to the Commissioner of Baseball of an Independent Investigation Into the Illegal Use of Steroids and Other Performance Enhancing Substances by Players in Major League Baseball.

This biographical article relating to an American baseball pitcher born in the 1960s is a stub.