T-Mobile Park is a retractable roof baseball park in Seattle, Washington, United States. Owned and operated by the Washington State Major League Baseball Stadium Public Facilities District, it is the home stadium of the Seattle Mariners of Major League Baseball (MLB) and has a seating capacity of 47,929 for baseball. It is in Seattle's SoDo neighborhood, near the western terminus of Interstate 90. The first game at the stadium was played on July 15, 1999.

During the 1990s, the suitability of the Mariners' original stadium—the Kingdome—as an MLB facility came under question, and the team's ownership group threatened to relocate the team. In September 1995, King County voters defeated a ballot measure to secure public funding for a new baseball stadium. Shortly thereafter, the Mariners' first appearance in the MLB postseason and their victory in the 1995 American League Division Series (ALDS) revived public desire to keep the team in Seattle. As a result, the Washington State Legislature approved an alternate means of funding for the stadium with public money. The site, just south of the Kingdome, was selected in September 1996 and construction began in March 1997. The bonds issued to finance Safeco Field were retired on October 1, 2011, five years earlier than anticipated.

T-Mobile Park is also used for amateur baseball events, including the Washington Interscholastic Activities Association high school state championships and one Washington Huskies game per season. Major non-baseball events that have been held at T-Mobile Park include the 2001 Seattle Bowl and WrestleMania XIX in 2003, which attracted the stadium's record attendance of 54,097.

The ballpark was originally named Safeco Field under a 20-year naming-rights deal with Seattle-based Safeco Insurance. Safeco declined to renew the agreement beyond the 2018 season. The naming rights were acquired by T-Mobile on December 19, 2018, with the name change taking effect January 1, 2019.

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