The original teams in the National League when it started in 1876 were:
- Chicago White Stockings (now known as the Cubs)
- St. Louis Brown Stockings (defunct after 1877 season)
- Hartford Dark Blues (defunct after 1877 season)
- Boston Red Caps (now the Atlanta Braves)
- Louisville Grays (defunct after 1877 season)
- New York Mutuals (expelled from the league after the 1876 season)
- Philadelphia Athletics (expelled from the league after the 1876 season)
- Cincinnati Red Stockings (expelled from the league after the 1880 season; helped start the American Association, later transferred back to N.L.)
Through the end of the 1800s, a lot of teams came and went in the NL. After the league contracted before the 1900 season, the teams remaining stayed the same for over 50 years. They were (with the current name in parentheses):
- Chicago Orphans (Cubs)
- Boston Beaneaters (Atlanta Braves)
- Brooklyn Superbas (L.A. Dodgers)
- Pittsburg(h) Pirates
- Philadelphia Phillies
- St. Louis Cardinals
- Cincinnati Reds
- New York Giants (S.F. Giants)
The AL was considered a major league as of 1901. Apart from 2 teams (noted below), they also stayed the same into the 1950s. The teams were:
- Chicago White Sox
- Boston Americans (Red Sox)
- Detroit Tigers
- Philadelphia Athletics (Oakland A's)
- Baltimore Orioles (N.Y. Yankees as of 1903)
- Washington Senators (Minnesota Twins)
- Cleveland Blues (Indians)
- Milwaukee Brewers (St. Louis Browns as of 1902, now the Baltimore Orioles)