The 1979–80 NHL season was the 63rd season of the National Hockey League. This season saw the addition of four teams from the disbanded World Hockey Association as expansion franchises. The Edmonton Oilers, Winnipeg Jets, New England Whalers (later renamed "Hartford Whalers" at the insistence of the Boston Bruins), and Quebec Nordiques joined the NHL, bringing the total to 21 teams. The other two WHA teams (Birmingham Bulls and Cincinnati Stingers) were paid to disband.

The New York Islanders won their first Stanley Cup, defeating the Philadelphia Flyers in six games, in the finals.

The season also marked the eighth and final season for the Flames in Atlanta before the franchise relocated to Calgary. The NHL would return to the Georgia capital in 1999 with the Thrashers, but that team would ultimately relocate away from Atlanta as well becoming the second (and current) incarnation of the Winnipeg Jets.

The collapse of the WHA also saw the much hyped super-star rookie Wayne Gretzky come to the NHL with the Edmonton Oilers. Gretzky would tie Marcel Dionne for the scoring lead with 137 points and capture the Hart Memorial Trophy as the most valuable player while Dionne took home the Art Ross Trophy as the leading scorer by virtue of having scored two more goals. Gretzky aside, many players made their debut in the NHL this season, both due to the WHA merger and to a change in the rules for the Entry Draft allowing eighteen- and nineteen-year-olds to be drafted for the first time; no fewer than seven Hall of Famers (Gretzky, Ray Bourque, Mark Messier, Mike Gartner, Michel Goulet, Mark Howe, and Joe Mullen; Mullen was undrafted) debuted this season along with numerous other perennial stars.

The big story of the regular season was the record-breaking undefeated streak compiled by the Philadelphia Flyers. After starting the season with a 5–2 win over the New York Islanders and a 9–2 loss to the Atlanta Flames, the Flyers did not lose again for nearly three months, earning at least one point in every game between a 4–3 win over Toronto on October 14, 1979, and a 4–2 win over Buffalo on January 6, 1980, a span of (record 25–0–10) 35 games. This stands as the longest undefeated streak in North American professional sports history.

With 21 teams in the league, the regular-season schedule was set without regard to divisional affiliation. Each team played each of the other 20 teams four times in the year, twice at home and twice on the road. As well, a new playoff structure was introduced with the four division winners plus the next 12 teams with the best records qualifying. Division winners were not granted any byes and the divisions were ignored for determining playoff match-up seeding. Thus the division grouping ensured that if the five worst teams were to be in the same five-team division, the winner of this division would have qualified for the playoffs despite having the 17th best season record. Except for that unlikely possibility the divisional affiliations were irrelevant and had no effect on playoff qualification or seeding. A few months into the season, the Detroit Red Wings started playing at Joe Louis Arena after having spent all but their first season at the Detroit Olympia.

For the four previous seasons, the Boston Bruins had owned first place in the Adams Division. This season saw the Buffalo Sabres dethrone the Bruins in the Adams. The New York Islanders finished first overall in the NHL the previous season with 116 points, but lost in the playoffs semifinals to the upstart New York Rangers. This season saw them fall considerably in the standings as they finished fifth overall with 91 points, a full 25 points below last year's finish. On the other hand, the Philadelphia Flyers improved by 21 points from the previous season. Their 35-game undefeated streak (25–0–10) propelled them to the best record in the NHL with 116 points.

All four expansion teams finished poorly with records below .500. The Hartford Whalers fared the best with 73 points and the Winnipeg Jets tied the Colorado Rockies for last overall with 51 points. Hartford (14th overall) and Edmonton (16th overall) qualified for the playoffs, but both teams were swept 3 games to 0 in their respective first-round playoff series.

In August 1979, John Ziegler, the NHL president, announced that protective helmets will be mandatory for all NHL players. "The introduction of the helmet rule will be an additional safety factor", he said. The only exception will be for players who signed their pro contracts prior to June 1, 1979. Those players under the exception who chose not to wear a helmet also had to sign a waiver form. At the time of the rule change, about 70% of NHLers were wearing helmets already. The first player to wear protective headgear on a regular basis was George Owen of the Boston Bruins in 1928. Prior to that, the only time protective headgear was worn was to temporarily protect injuries. Craig MacTavish, while playing for the St. Louis Blues, was the last helmetless player, retiring after the 1996–97 season.

Note: GP = Games played, W = Wins, L = Losses, T = Ties, Pts = Points, GF = Goals for, GA = Goals against, PIM = Penalties in minutes

Note: Teams that qualified for the playoffs are highlighted in bold

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With the league expansion from 17 to 21 teams, the playoffs were also expanded, from a 12-team tournament to a 16-team tournament. The sixteen teams were composed of the four divisional champions plus the top 12 finishers of the remaining 17 teams. The 16 qualifying teams were then seeded based on regular season points, with divisional rankings ignored. Division leaders no longer received first round byes. The teams were seeded 1 through 16, with the top team playing the 16th team in the first round, and so on. In subsequent rounds, matchups were similarly arranged, with the top remaining seed against the lowest remaining seed, and so on. The Preliminary Round was a best-of-five set.^[2] The Atlanta Flames played their final playoff games in this postseason, and moved to Calgary soon after, the playoffs returned to Atlanta in 2007.

The sixteen teams that qualified for the playoffs are ranked 1–16 based on regular season points.

The story of the playoffs was Mike Bossy and the New York Islanders. After a dismal start for their franchise in the early seventies, the Islanders built a contender for the Stanley Cup and won their first of four in a row by beating the Philadelphia Flyers in overtime of game six of the final. Defenceman Denis Potvin scored a crucial overtime goal in game one and the Cup was won when Bobby Nystrom scored the Cup-winning goal from John Tonelli and Lorne Henning at 7:11 of the first overtime. Ken Morrow became the first hockey player in history to win an Olympic Gold Medal and the Stanley Cup in the same season. Hall of Fame announcer Dan Kelly was calling the play-by-play for CBS Sports on that day, May 24, 1980. It was the last NHL game to air on American network television for nearly ten years.^[3]

Note: GP = Games played; G = Goals; A = Assists; Pts = Points

Source: NHL.^[4]

Note: GP = Games played; Min = Minutes Played; GA = Goals Against; GAA = Goals Against Average; W = Wins; L = Losses; T = Ties; SO = Shutouts

The following is a list of players of note who played their first NHL game in 1979–80 (listed with their first team, asterisk(*) marks debut in playoffs):

Players marked with § previously started their major professional career in the World Hockey Association.

The following is a list of players of note that played their last game in the NHL in 1979–80 (listed with their last team):