| Season(s) | Notes and Changes |
|---|---|
| 1917-18 | The NHL's inauagural season. Four teams begin the campaign, but the Montreal Wanderers fold after their arena burns down. |
| 1918-19 | A three-team NHL, consisting of Montreal, Ottawa, and Toronto. |
| 1919-20 | A charter member that was mothballed for two seasons, the Quebec Bulldogs, finally begins operation. |
| 1920-21 - 1923-24 | The Quebec franchise is transferred to Hamilton and is renamed the Tigers. |
| 1924-25 | The first two expansion teams in NHL history, the Boston Bruins and Montreal Maroons, begin play. |
| 1925-26 | Further expansion to New York and Pittsburgh. The Americans and Pirates are the second and third US-based teams, while the Hamilton Tigers fold. |
| 1926-27 - 1929-30 | Three new teams are added, the Rangers, Black Hawks, and Cougars (later the red Wings), successful franchises to the present. The ten-team league is split into the American and Canadian divisions. |
| 1930-31 | The Pittsburgh Pirates, facing financial difficulty, are transferred to Philadelphia and renamed the Quakers. |
| 1931-32 | The Pittsburgh/Philadelphia franchise finally folds, Ottawa suspends operations for one year, and the Detroit Cougars are renamed the Falcons. |
| 1932-33 - 1933-34 | Ottawa is taken out of mothballs and the Detroit Falcons take their famous moniker - the Red Wings. |
| 1934-35 | The struggling Ottawa franchise is moved to St. Louis. The Eagles, quite a distance from other NHL cities, last only one season. |
| 1935-36 - 1937-38 | St. Louis (formerly the once-mighty Ottawa Senators) fold. |
| 1938-39 - 1940-41 | The Montreal Maroons fold, leaving a seven-team league (three Canadian, four American). Divisional play is abandoned until 1967. |
| 1941-42 | The struggling New York Americans attempt to survive by taking the name Brooklyn Americans. They still play at Madison Square Garden but practice in Brooklyn. The unsuccessful marketing experiment lasts one season. |
| 1942-43 - 1966-67 | The Golden Age of Hockey: The Original Six remain after the Americans fold and the league is unchanged for 25 years. |
| 1967-68 - 1969-70 | After the first expansion: The NHL doubles, with the Original Six in the East Division, and the new teams in the West Division. |
| 1970-71 - 1971-72 | The Buffalo Sabres and Vancouver Canucks are added to the East, and Chicago moves to the West. |
| 1972-73 - 1973-74 | The New York Islanders are added to the East and Atlanta Flames to the West. |
| 1974-75 - 1975-76 | With new teams in Kansas City and Washington, the League divides into the Wales and Campbell Conferences. Divisions are named after Lester Patrick, Charles F. Adams, Conn Smythe, and James Norris, Sr. |
| 1976-77 - 1977-78 | California moves to Cleveland and Kansas City scouts out the Colorado Rockies. |
| 1978-79 | The Barons are merged with the North Stars, and Minnesota moves to the Adams Division. |
| 1979-80 | The remaining WHA clubs are added: Edmonton, Hartford, Quebec, and Winnipeg. |
| 1980-81 | The league in the season following the Flames move north from Atlanta to Calgary. |
| 1981-82 | The Conferences and Divisions are realigned. |
| 1982-83 - 1990-91 | The NHL remains constant for nine years following the Rockies move to New Jersey. |
| 1991-92 | The San Jose Sharks join the League as the Smythe Division's sixth team. |
| 1992-93 | Four balanced divisions: The Ottawa Senators join the Adams Division, and the Tampa Lightning are added to the Norris. |
| 1993-94 - 1994-95 | The Minnesota North Stars become the Dallas Stars, the League scraps the old Conference and Division names for NBA-style regional, meaningless names, and the Florida Panthers and Anaheim Mighty Ducks become the 25th and 26th teams. |
| 1995-96 | The Quebec Nordiques move to Colorado, giving the Pacific Division seven teams and balancing the Conferences. |
| 1996-97 | The Jets fly from Winnipeg to Pheonix, and the Coyotes remain in the Central Division. |