Jason Michael Johnson (born October 27, 1973 in Santa Barbara, California) is a right-handed starting pitcher for the Boston Red Sox in Major League Baseball. He is six foot six (1.98 m), 217 lb (98 kg), and bats right-handed.

Johnson did not go to college, and was signed by the Pittsburgh Pirates as an undrafted free agent in 1992. After debuting with the Pirates in 1997, he has gone on to play for the Tampa Bay Devil Rays, Baltimore Orioles, Detroit Tigers, and Cleveland Indians. He has the distinction of being the first Tigers pitcher to hit a home run in a regular season game since 1971 (when Les Cain hit one), when he went deep on June 8, 2005, against Los Angeles Dodgers pitcher Jeff Weaver, at Dodger Stadium.

After enduring two losing seasons with Detroit, Johnson signed with Cleveland prior to the 2006 season. He fared no better there, and was designated for assignment on June 22, 2006. Before he decided whether or not to accept the assignment, he was traded to Boston for a player to be named later and/or cash.

Johnson has diabetes and was the first Major League Baseball player ever to be allowed to wear an insulin pump on the field, which regulates the amount of insulin pumped into his body. The pump is attached to his belt on the left side of his lower back, in order to minimize the chance of it being hit by a batted or thrown ball.

In 2001, he received the Tony Conigliaro Award.

As a pitcher, Johnson is capable of eating up innings and enduring higher-than-normal pitch counts (consistently over 100 over the past few years).