The National Hockey League (NHL) first held a regular season outdoor ice hockey game in 2003, and since 2008 the league has scheduled at least one per year.
The NHL primarily uses three brands for outdoor games: the Heritage Classic, Winter Classic, and Stadium Series. The 2003 Heritage Classic between the Edmonton Oilers and Montreal Canadiens was the first outdoor regular season game in NHL history. The Heritage Classic has since been held infrequently in football stadiums in Canada, featuring match-ups solely between Canadian teams, until the Buffalo Sabres make their appearance in the 2022 Heritage Classic. The annual Winter Classic, held on New Year's Day in football or baseball stadiums near NHL home markets in the United States, began with the 2008 game between the Pittsburgh Penguins and the Buffalo Sabres. The NHL then started the Stadium Series in 2014 for additional outdoor games in the United States. The number of Stadium Series games has varied per season (four in 2014, only one in 2015, two in 2016, and one per season since 2017). Both the Winter Classic and the Stadium series featured match-ups solely between American teams until the Toronto Maple Leafs' appearances in both the 2014 Winter Classic and the 2018 Stadium Series.
To celebrate the NHL's 100 year anniversary in 2017, the league scheduled two special outdoor games: the NHL Centennial Classic between Detroit and Toronto on January 1 (through season 2016–2017) to kick off the year, and then the NHL 100 Classic on December 16 (during 2017–2018 season) between Montreal and the Ottawa Senators to commemorate the league's first game, having taken place exactly 100 years before, between the same contenders. The four teams involved in said honorific matches constitute four of the league's Original Six members. Then in 2021 due to the COVID-19 pandemic, the league held the NHL Outdoors at Lake Tahoe, two outdoor games played without spectators.
Prior to 2003, NHL teams had been involved in at least three outdoor exhibitions. Two of these came in the 1950s and were effectively informal scrimmages; in 1954, the Detroit Red Wings visited Marquette Branch Prison and played a match against the prison inmates in a fenced-off, open air ice rink, while in 1956, the Boston Bruins played a game against several local teams in Bay Roberts, Newfoundland. In neither case was a formal game structure maintained or score kept, as the NHL teams hopelessly outmatched the hosts. In 1991, the Los Angeles Kings and New York Rangers played a pre-season game outside Caesars Palace in Las Vegas, in the first officially sanctioned outdoor NHL contest.
The NHL's outdoor series have proven wildly popular with fans and have led to numerous attendance records. The 2003 Heritage Classic drew 57,167 fans, a league record that stood until 71,217 fans in Buffalo set another NHL record in the inaugural Winter Classic in 2008. The 2014 Winter Classic, between Toronto and the Detroit Red Wings drew 105,491 fans, the current NHL record.