The 1956–57 NHL season was the 40th season of the National Hockey League. Six teams each played 70 games. The Montreal Canadiens won the Stanley Cup for the second consecutive season, defeating the Boston Bruins four games to one in the best-of-seven final series. The final game was won with a clutch goal from Montreal defenceman Tom Johnson that clinched the Stanley Cup championship for the Canadiens 3–2.

On October 1, it was announced that Dick Irvin had resigned as coach of the Chicago Black Hawks due to ill health. He was suffering from bone cancer and had been ill for two years and had been hospitalized in Montreal. Irvin had been several days late to training camp. General manager Tommy Ivan took over as coach. Later in the season, it was reported that Irvin had undergone minor surgery for anemia at Ross Memorial Hospital. Irvin died on May 15, 1957.

Ted Lindsay, the star left winger of the Detroit Red Wings, became the fourth player to score 300 career goals on November 18, when he picked up two goals in an 8–3 pasting of the Montreal Canadiens. The other players to reach this prestigious mark were Nels Stewart, Maurice Richard, and Gordie Howe (who played opposite Lindsay for most of the latter's career).

On January 5, the Black Hawks and New York Rangers played an afternoon game at Madison Square Garden where the Rangers beat the Black Hawks 4–1. This game was broadcast on the Columbia Broadcast System network (CBS). Glen Skov spoiled Lorne "Gump" Worsley's would-be shutout with a goal in the third period.

Montreal beat Toronto 2–1 at the Forum in Montreal on January 10 and moved into first place. The game was hard-fought and referee Frank Udvari found it necessary to rule with an iron hand that angered the fans. Fans thought he was calling chippy penalties against the Habs and deliberately failing to call hooking and holding penalties by the Maple Leafs. The blow-off came in the last two minutes of the game. Maurice Richard received a high-sticking penalty. At 18:14, knowing his Maple Leafs were in danger, Toronto coach Howie Meeker pulled goaltender Ed Chadwick for six attackers. Dick Duff scored the tying goal, and Richard went berserk and commenced a heated argument with Udvari, banging his stick on the ice. He might have attacked Udvari if his teammates had not restrained him. Fans threw programmes, paper cups, hats and other debris and the game was held up. When it did resume, Bernie "Boom Boom" Geoffrion set up Don Marshall for the winning goal with a mere six seconds left to play. Although the fans were pleased with the outcome, an angry hum commenced as the players and officials left the ice. Udvari had to be escorted to his dressing room by police and ushers. A large part of the crowd now directed its attention to NHL President Clarence Campbell seated in his box seat and he became the target of jeers and threats. The situation began to show some of the aspects of the Richard Riot of two years previous when Richard had been suspended for an attack on an official. It was at least 30 minutes before Campbell was able to leave under police protection.

Terry Sawchuk had been playing well and was a candidate for the Hart Trophy, when he came down with mononucleosis. He came back too soon and by January 16, he announced his retirement from hockey, a temporary one as he would be back in Detroit next season.

Glenn Hall was not as good as the previous season, but led the Detroit Red Wings to first place. Hall had played only two games prior to 1955–56, but had shown such promise Sawchuk was sent off.

• Boston Bruins: Milt Schmidt
• Chicago Black Hawks: Tommy Ivan
• Detroit Red Wings: Jimmy Skinner
• Montreal Canadiens: Toe Blake
• New York Rangers: Phil Watson
• Toronto Maple Leafs: Howie Meeker

The following is a list of players of note who played their first NHL game in 1956–57 (listed with their first team, asterisk(*) marks debut in playoffs):

• Larry Regan, Boston Bruins
• Moose Vasko, Chicago Black Hawks
• Ralph Backstrom, Montreal Canadiens
• Phil Goyette, Montreal Canadiens
• Frank Mahovlich, Toronto Maple Leafs
• Bob Pulford, Toronto Maple Leafs
• Bob Baun, Toronto Maple Leafs

The following is a list of players of note that played their last game in the NHL in 1956–57 (listed with their last team):

• Cal Gardner, Boston Bruins
• Harry Watson, Chicago Black Hawks
• Marty Pavelich, Detroit Red Wings
• Gerry McNeil, Montreal Canadiens
• Ted Kennedy, Toronto Maple Leafs

Hockey Night in Canada on CBC Television televised Saturday night regular season games and selected Stanley Cup playoff games. Games were not broadcast in their entirety until the 1968–69 season, and were typically joined in progress, while the radio version of HNIC aired games in their entirety.

In the U.S., CBS signed a four-year deal to televise Saturday afternoon games from January to March.

• 1956–57 NHL transactions
• 1956 NHL Intra-League Draft
• List of Stanley Cup champions
• National Hockey League All-Star Game
• 1956 in sports
• 1957 in sports