- Founded: 1977
- Home ballpark: Safeco Field, Seattle
- Uniform colors: Blue and White
- Logo design: A baseball on an 8-pointed compass.
- League pennants won: None
- World Series championships won: None
The team were added to the American League in 1977, and were for many years perennial non-achievers. By the mid 1990s, under manager Lou Piniella, with a core of strong players built around center-fielder Ken Griffey Jr, pitcher Randy Johnson and designated hitter Edgar Martinez, they won their division in 1995. Their dramatic championship run that year was halted in the ALCS by the Cleveland Indians. They won the division again in 1997 and the playoff wild card in 2000, despite the loss of Griffey and Johnson.
In 2001, despite the loss of superstar shortstop Alex Rodriguez, with the addition of Japanese sensation Ichiro the Mariners had one of the most successful regular seasons on record, leading the major leagues in winning percentage from start to finish, winning the American League West championship easily, setting a new American League record for most wins in a single season (116), and matching the major league record for single season wins set by the Chicago Cubs in 1906. They pulled off a come-from-behind 3-2 series win over the Cleveland Indians in the ALDS to advance to the American League Championship Series against the New York Yankees, but succumbed to the Yankees for the second year in a row in the ALCS, 4 games to 1.
Seattle's previous major league team, the Pilots, became the Milwaukee Brewers in 1970, after a single season in Seattle.
Players of note
- Baseball Hall of Famers: none yet
- Current stars: Edgar Martinez, Jay Buhner, Ichiro Suzuki, Bret Boone (currently Free Agent), Freddie Garcia, Jamie Moyer, Kazuhiro Sasaki, John Olerud, Mike Cameron, Jeff Nelson
- Not to be forgotten: Ken Griffey Jr, Randy Johnson (AL Cy Young Award 1995), Alex Rodriguez
- Retired numbers: #42 Jackie Robinson