The 2004-05 NHL season would have been the 88th regular season of the National Hockey League (NHL). The season 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 made the NHL the first North American professional sports league to cancel an entire season because of a labour dispute. It was also the first time since 1919 that the Stanley Cup was not awarded. In 1919, the championship was canceled due to an outbreak of Influenza.

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 through a key 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.