| 1902 | Milwaukee Brewers (1st) became St Louis Browns (current Orioles) |
| 1902 | Cleveland Blues became Cleveland Bronchos (current Indians) |
| 1903 | Baltimore Orioles (1st) became New York Highlanders (current Yankees) |
| 1903 | Cleveland Bronchos became Cleveland Naps (current Indians) |
| 1903 | Chicago Orphans became Chicago Cubs |
| 1907 | Boston Beaneaters became Boston Doves (current Braves) |
| 1908 | Boston Americans became Boston Red Sox |
| 1911 | Boston Doves became Boston Rustlers (current Braves) |
| | |
| 1912 | Boston Rustlers became Boston Braves |
| 1913 | New York Highlanders became New York Yankees |
| 1914 | Brooklyn Superbas became Brooklyn Robins (current Dodgers) |
| 1915 | Cleveland Naps became Cleveland Indians |
| | |
| 1932 | Brooklyn Robins became Brooklyn Dodgers |
| 1936 | Boston Braves became Boston Bees |
| 1941 | Boston Bees became Boston Braves |
| | |
| 1943 | Philadelphia Phillies became Philadelphia Blue Jays |
| 1945 | Philadelphia Blue Jays became Philadelphia Phillies |
| 1946 | World Series went to 2-3-2 format |
| | |
| 1953 | Boston Braves became Milwaukee Braves |
| 1953 | Cincinnati Reds became Cincinnati RedLegs |
| 1954 | St Louis Browns became Baltimore Orioles |
| 1955 | Philadelphia A's became Kansas City A's |
| 1958 | Brooklyn Dodgers became Los Angeles Dodgers |
| 1958 | New York Giants became San Francisco Giants |
| 1959 | Cincinnati RedLegs became Cincinnati Reds |
| | |
| 1961 | Washington Senators (1st) became Minnesota Twins |
| 1961 | Los Angeles Angels and new Washington Senators (2nd) began play |
| 1962 | New York Mets and Houston Colt .45s began play |
| 1965 | Houston Colt .45s became Houston Astros |
| 1965 | Los Angeles Angels became California Angels |
| 1966 | Milwaukee Braves became Atlanta Braves |
| 1968 | Kansas City A's became Oakland A's |
| 1969 | Each league separated into an East and West division |
| 1969 | Montreal Expos and San Diego Padres began play |
| 1969 | Seattle Pilots and Kansas City Royals began play |
| | |
| 1970 | Seattle Pilots became Milwaukee Brewers |
| 1972 | Washington Senators (2nd) became Texas Rangers |
| 1977 | Toronto Blue Jays and Seattle Mariners began play |
| | |
| 1985 | Division playoffs went from best-of-five to best-of-seven |
| | |
| 1993 | Colorado Rockies and Florida Marlins began play |
| 1994 | Each league became East, Central, and West divs with wild-card teams |
| 1997 | California Angels became Anaheim Angels |
| 1998 | Arizona Diamondbacks and Tampa Bay Devil Rays began play |
| 1998 | Milwaukee Brewers switched from AL Central to NL Central |
| 1998 | Detroit Tigers switched from AL East to AL Central |
| | |
| 2005 | Montreal Expos became Washington Nationals |
| 2005 | Anaheim Angels became Los Angeles Angels |
| 2008 | Tampa Bay Devil Rays became Tampa Bay Rays |
| | |
| 2012 | Florida Marlins became Miami Marlins |
| 2012 | Second wild card team added in each league |
| 2013 | Houston Astros moved from the NL Central to the AL West |
| |
| 2022 | Cleveland Indians became Cleveland Guardians |
| 2022 | Third wild card team with WC round and div series to five games |
| 2025 | Oakland A's became the A's |
| |
| List of abbreviations used in other pages: |
| Anaheim | Ana | Anaheim Angels (1997 - 2004) |
| Arizona | Ari | Arizona Diamondbacks (1998 - present) |
| As | As | As (2025 - present) |
| Atlanta | Atl | Atlanta Braves (1966 - present) |
| Bal Orioles | BlO | Baltimore Orioles (1st) (1901 - 1902) |
| Baltimore | Bal | Baltimore Orioles (1954 - present) |
| Bos Americans | BsA | Boston Americans (1901 - 1907) |
| Bos Beaneaters | BBn | Boston Beaneaters (1901 - 1906) |
| Bos Bees | BBe | Boston Bees (1936 - 1940) |
| Bos Braves | BsB | Boston Braves (1911-1935, 1941-1952) |
| Bos Doves | BsD | Boston Doves (1907 - 1908) |
| Bos Rustlers | BsR | Boston Rustlers (1909 - 1910) |
| Boston | Bos | Boston Red Sox (1908 - present) |
| Bkn Robins | BkR | Brooklyn Robins (1914 - 1931) |
| Bkn Superbas | BkS | Brooklyn Superbas (1901-1910, 1913) |
| Brooklyn | Bkn | Brooklyn Dodgers (1911-1912, 1932-1957) |
| California | Cal | California Angels (1965 - 1996) |
| Chi Cubs | ChC | Chicago Cubs (1903 - present) |
| Chi Orphans | ChO | Chicago Orphans (1901 - 1902) |
| Chi White Sox | ChW | Chicago White Sox (1901 - present) |
| Cincinnati | Cin | Cincinnati Reds (1901 - present) |
| Cin Redlegs | CRL | Cincinnati Redlegs (1953 - 1958) |
| Cle Blues | CBl | Cleveland Blues (1901 - 1901) |
| Cle Bronchos | CBr | Cleveland Bronchos (1902 - 1902) |
| Cle Naps | ClN | Cleveland Naps (1903 - 1914) |
| Cleveland | Cle | Cleveland Indians (1915 - 2021) |
| Cleveland | Cle | Cleveland Guardians (2022 - present) |
| Colorado | Col | Colorado Rockies (1993 - present) |
| Detroit | Det | Detroit Tigers (1901 - present) |
| Florida | Fla | Florida Marlins (1993 - 2011) |
| Hou Colt .45s | HoC | Houston Colt .45s (1962 - 1964) |
| Houston | Hou | Houston Astros (1965 - present) |
| Kansas City As | KCA | Kansas City A's (1955 - 1967) |
| Kansas City | KC | Kansas City Royals (1969 - present) |
| LA Angels | LAA | Los Angeles Angels (1961-1964, 2005-present) |
| LA Dodgers | LAD | Los Angeles Dodgers (1958 - present) |
| Miami | Mia | Miami Marlins (2012 - present) |
| Mil Braves | MlB | Milwaukee Braves (1953 - 1965) |
| Mil Brewers | MlW | Milwaukee Brewers (1st) (1901) |
| Milwaukee | Mil | Milwaukee Brewers (1970 - present) |
| Minnesota | Min | Minnesota Twins (1961 - present) |
| Montreal | Mtl | Montreal Expos (1969 - 2004) |
| NY Giants | NYG | New York Giants (1901 - 1957) |
| NY Highlanders | NYH | New York Highlanders (1903 - 1912) |
| NY Mets | NYM | New York Mets (1962 - present) |
| NY Yankees | NYY | New York Yankees (1913 - present) |
| Oakland | Oak | Oakland A's (1968 - 2024) |
| Philadelphia As | PhA | Philadelphia A's (1901 - 1954) |
| Phi Blue Jays | PhB | Philadelphia Blue Jays (1943 - 1944) |
| Philadelphia | Phi | Philadelphia Phillies (1901 - present) |
| Pittsburgh | Pit | Pittsburgh Pirates (1901 - present) |
| San Diego | SD | San Diego Padres (1969 - present) |
| San Francisco | SF | San Francisco Giants (1958 - present) |
| Sea Pilots | SeP | Seattle Pilots (1969) |
| Seattle | Sea | Seattle Mariners (1977 - present) |
| St Louis | StL | St Louis Cardinals (1901 - present) |
| StL Browns | StB | St Louis Browns (1902 - 1953) |
| TB Devil Rays | TBD | Tampa Bay Devil Rays (1998 - 2007) |
| Tampa Bay | TB | Tampa Bay Rays (2008 - present) |
| Texas | Tex | Texas Rangers (1972 - present) |
| Toronto | Tor | Toronto Blue Jays (1977 - present) |
| Washington | Wsh | Washington Nationals (2005 - present) |
| Wash Senators | WSn | Washington Senators (1st) (1901 - 1960) |
| Was Senators | WsS | Washington Senators (2nd) (1961 - 1971) |
