The Devil Rays entered the American League in 1998, prompting the Milwaukee Brewers to change leagues to make room. Their fellow expansion team was the National League's Arizona Diamondbacks, who have been far more successful in the early going.

The Rays were the first expansion team to enter the AL since the Mariners and Blue Jays were added in 1977. The first few years of Tampa history were no more successful than those two teams early years. The Rays also became the first team to hold spring training in their home city, training in St. Petersburg. In that first season the D-Rays avoided 100 losses - by a single game. The season wasn't a complete bust - on April 19 their record was 10-6, making them the first expansion team to ever be four games over .500 at any point in their first season.

The most exciting event in franchise history came in 1999 when Wade Boggs homered for his 3,000th hit on August 7, 1999 in Tropicana Field. McGriff also reached a milestone as a Devil Ray - slugging his 400th homer on June 2, 2000. Boggs retired after the 1999 season and was hired as team hitting coach. He later resigned after the 2001 season.

Early in 2001, with the Rays record at 4-10, manager Larry Rothschild (205-294 in three-plus years) was axed in favor of Hal McRae. The move helps little, as the franchise suffered it's first 100-loss campaign and ran dead last for the fourth straight season. On April 19, 2001 pitcher Travis Phelps made his ML debut at Tropicana Field, working two scoreless innings against the Boston Red Sox. Phelps, drafted in the 89th round of the 1996 draft, became the lowest-selected player to ever reach the big leagues. In May, with the strong blessing of commissioner Bud Selig's office, the Devil Rays brought John McHale Jr. in as the new COO. The move was prompted by the team's efforts to build a new stadium, McHale's specialty.

In 2004 the Tampa Bay Devil Rays finished in 4th place in the American League East Division with a 70-91 record.

In 2006 Tampa Bay finished with a 61-101 record, last place and worst record in baseball.