Carlos Alfonso Guillén (born September 30, 1975 in Maracay, Aragua State, Venezuela) is a Major League Baseball second baseman and switch-hitter for the Detroit Tigers.
Guillén was signed by the Houston Astros as a non-draft amateur free agent in 1992. He was traded to the Seattle Mariners with pitcher Freddy García and John Halama in the deal that sent Randy Johnson to the Astros. Guillén made his debut in 1998 and was traded to Detroit at the end of the 2003 season.
In Seattle, Guillén was initially forced to play second and third base with incumbent Alex Rodriguez at shortstop. After Alex Rodriguez signed with the Texas Rangers for the 2000 season, Guillén moved back to his natural position. He had a league-average campaign in his first full season with the club.