Jason Raymond Bay, (born September 20, 1978, in Trail, British Columbia) is a Canadian-American Major League Baseball outfielder for the Boston Red Sox.

Bay experienced success as a player very early, playing on a Trail team that reached the 1990 Little League World Series. In 1999 he played for the Chatham Athletics in the Cape Cod Baseball League. He was drafted by the Montreal Expos in the 22nd round of the 2000 Major League Baseball Draft from Gonzaga University and was assigned to the Expos' Short-Season A team in Burlington, Vermont (The Vermont Expos). In 2001, Bay was assigned to the Expos’ High Single-A team in Jupiter. He began the year slowly, and in May he was moved to Clinton of the Midwest League. Bay reached base in his first 26 games, then went on to hit .362 and win the league batting title. In all, he batted .315 with 14 homers and 75 RBIs on the year. He was dealt to the New York Mets on March 24, 2002, for Lou Collier. The Mets dealt him to the San Diego Padres for Jason Middlebrook at the 2002 trading deadline. He debuted with the Padres on May 23, 2003, getting his first major league hit, a home run, in the 9th inning. Two days later, he suffered a broken right wrist after a hit by pitch.

On August 26, 2003, Bay was traded to the Pittsburgh Pirates, along with Óliver Pérez and Cory Stewart in August in exchange for Brian Giles. He finished the season with a .287 batting average, four home runs, and 14 RBI in 30 games.