The 2004–05 NHL season was the National Hockey League's 88th season of operation. The entire 1,230-game schedule, that was to begin in October, was officially canceled on February 16, 2005 due to an unresolved lockout that began on September 16, 2004. The loss of the 2004–05 season's games made the NHL the first North America professional sports league to lose an entire season of games because of a labor dispute. It was the first time since 1919, when a Spanish flu pandemic canceled the playoffs, that the Stanley Cup was not awarded. This canceled season was later acknowledged with the words "2004–05 Season Not Played" engraved on the Cup.
According to the International Ice Hockey Federation, 388 NHL players were on teams overseas at some point during the season, spread across 19 European leagues. Many of these players had a contract clause to return to the NHL when the league started up again, even if it was during the current season.
Key rule changes which would dominate after the lockout were established as a result of a meeting between the NHL and its top minor league, the American Hockey League. On July 5, 2004, the AHL announced publicly the 2004–05 rule changes, many of which were passed as a result of the NHL's recommendation for experimentation.