1977 Major League Baseball expansion

The 1977 Major League Baseball expansion resulted in the establishment of expansion franchises in Seattle and Toronto in the American League of Major League Baseball. The Seattle Mariners and Toronto Blue Jays began play in the 1977 Major League Baseball season, becoming the 25th and 26th teams in Major League Baseball.

Seattle and Toronto were included in a list of potential expansion cities in a survey conducted by the American League in 1960. The others were Atlanta, Buffalo, Dallas–Fort Worth, Denver, Oakland, and San Diego (all of which received MLB franchises eventually through expansion or relocation except Buffalo, which has an AAA team, however).