The Seattle Mariners farm system consists of six Minor League Baseball affiliates across the United States and in the Dominican Republic.
The Mariners have been affiliated with the Triple-A Tacoma Rainiers of the Pacific Coast League and High-A Everett AquaSox of the Northwest League since 1995, making them the longest-running affiliations in the organization among teams not owned by the Mariners.
Geographically, Seattle's closest domestic affiliate is the Tacoma Rainiers, which are approximately 26 miles (42 km) away.
[1] Prior to the 1963 season, Major League Baseball (MLB) initiated a reorganization of Minor League Baseball that resulted in a reduction from six classes to four (Triple-A, Double-A, Class A, and Rookie) in response to the general decline of the minors throughout the 1950s and early-1960s when leagues and teams folded due to shrinking attendance caused by baseball fans' preference for staying at home to watch MLB games on television.
[2] The current structure of Minor League Baseball is the result of an overall contraction of the system beginning with the 2021 season.