The National Hockey League (NHL) was established at Montréal on 26 November 1917. The original teams were the Montreal Canadiens, Montreal Wanderers, Ottawa Senators and Toronto Arenas; Québec held a franchise but decided not to operate that season. In the next 25 years the league underwent numerous changes in composition, scheduling and playoff format. The Boston Bruins were the first American club to join (1924); by 1926, 6 of the 10 teams were from the US. In 1942 there were 6 teams left (Montreal, Toronto Maple Leafs, Boston, Chicago Black Hawks, Detroit Red Wings and New York Rangers) and the league remained unchanged until 1967, when 6 new US-based teams were added (California - later Oakland - Seals, Los Angeles Kings, Minnesota North Stars, Philadelphia Flyers, Pittsburgh Penguins and St Louis Blues). The Buffalo Sabres and the Vancouver Canucks joined in 1970 and the Atlanta Flames and New York Islanders in 1972.

The number of teams reached 18 by 1974 (with the addition of the Kansas City Scouts and Washington Capitals), of which only 3 were based in Canada. One team folded in 1978 but the Hartford Whalers, Edmonton Oilers, Québec Nordiques and Winnipeg Jets joined the following year after the collapse of the World Hockey Association. The Atlanta franchise moved to Calgary in 1980 (the Calgary Flames), bringing the number of NHL teams in Canada to 7.

Further expansion in 1991 and 1992 increased the league to 26 teams, including another Canadian franchise, the Ottawa Senators. Franchises were also awarded to Tampa Bay (Lightning), Anaheim (Mighty Ducks), Miami (Florida Panthers) and San Jose (Sharks). The Nordiques, suffering financially from playing in the league's smallest market, were sold in 1995 and relocated to Denver, where they became the Avalanche. The Jets were also relocated in 1996, after being sold to a group in Phoenix. Renamed the Phoenix Coyotes (now Arizona Coyotes (2014)), a version the Jets franchise lived on in Arizona leaving 6 franchises operating in Canada. In the summer of 1997, the league announced that it would expand to 4 more American cities. By the year 2000, with the addition of the Nashville Predators (1998), Atlanta Thrashers (1999), Minnesota Wild and Columbus Blue Jackets (2000), the NHL had expanded to 30 teams. In 2011, the Atlanta Thrashers relocated to Winnipeg, and the Jets name was reinstated.

The fate of Canadian teams in the NHL, which are increasingly pressured to compete financially with American markets, is unsettling. Toronto was the only Canadian team in 2000 that consistently played to sell-out crowds. The NHL's Canadian Assistance Program offers aid only when teams can demonstrate their viability, and for most teams in Canada, viability is continually threatened by declining attendance. In 1999, Rod Bryden, owner of the Ottawa Senators, announced that unless the federal government was willing to offer financial support, the Senators would be the next Canadian team sold to the US. A startling announcement in January 2000 outlined how the federal government would offer annual aid to Canadian hockey teams until 2004. Widespread criticism of the proposal, however, was so severe that it brought about an immediate retraction.

In 2004 team owners enforced a lockout banning members of the NHL Players' Association (hockey players) from play. The lockout, a result of the players' resistance to a salary cap, lasted 310 days from 16 September 2004 to 13 July 2005. The result was a salary cap of $39 million (US) per team and a significant reduction in players' salaries. It was the first time a major North American sports league had lost an entire season due to a labour dispute. It also resulted in cancellation of the Stanley Cup playoffs, and for second time in its history the cup was not awarded. However, when the 2005 collective bargaining agreement expired in 2012 a new agreement could not be reached and the league locked out players once more. The impasse left the sport reeling once again, in danger of cancelling an entire season for the second time in a decade.

In recent years, the number of players in the NHL recruited from Canadian junior hockey have dropped from 70% to near 50%, as an increasing number of players, including many of the brightest stars, are coming from Sweden, Finland, the Czech Republic and the US.

Though the league has struggled, like most professional sports organizations, with strikes and soaring salaries and ticket prices, it remains the premier professional Hockey league in the world. The Stanley Cup, awarded exclusively to NHL teams since the 1926-27 season, is emblematic of the world professional championship.