Ryan Stewart Theriot (pronounced /ˈtɛrioʊ/) (born December 7, 1979 in Baton Rouge, Louisiana) is a Major League Baseball infielder for the Chicago Cubs.

After playing for Broadmoor High School in Baton Rouge, he played college baseball at Louisiana State University, and was named to the College World Series all-tournament team in 2000. On June 12, 2000, Theriot broke up a no-hitter that was being thrown by his future teammate, Mark Prior, then pitching for Southern Cal. A shortstop in college, Theriot was converted to second base for his major league debut, but primarily played shortstop throughout the 2007 season, and has been the every-day shortstop for the Cubs for the 2008 season. Theriot has also played third base, right field, and left field.

Theriot made his Major League Baseball debut on September 13, 2005, as a pinch hitter against the Cincinnati Reds, and gained his first hit the following day against Brian Shackelford. In 2006 he split time between the Iowa Cubs and the major league team, hitting .328 in 53 games with the Chicago team.