U20 World Championship, Knockout Stage

The first official tournament was held in 1977, although the first three tournaments were held unofficially from 1974 to 1976. The tournament has been dominated by the teams from Canada and Soviet Union/CIS/Russia, together accounting for 33 of the 48 overall gold medals awarded (through 2024). The USSR won the first four official tournaments, while the Canadians put together five straight championships between 1993 and 1997, and another five straight from 2005 to 2009. Canada leads the all-time gold medal count with 20 golds, while the Soviet Union, the CIS, and Russia combined have 13 golds.

When it began, the World Junior Championship was a relatively obscure tournament. It has since grown in prestige, particularly in Canada, where the tournament ranks as one of the most important events on the sports calendar and during the holiday season. The Globe and Mail writer Bruce Dowbiggin credits TSN, along with Canada's strong performance at the tournament, for turning it from an obscure non-event when it acquired the rights in 1991 (which had started to grow in prominence due to the 1987 Punch-up in Piestany) to one of Canada's most beloved annual sports events, and at the same time cementing the link between Canadian nationalism and hockey, and inspiring the NHL's Winter Classic. Based on increasing attendances for countries repeatedly hosting the event, the popularity of the tournament seems to be growing in other nations as well.

At editions of the tournament held in the country, games involving Team Canada consistently sell out NHL arenas, offering large profit guarantees to Hockey Canada and the IIHF. In the 21st century, Canada has and will continue to host the tournament every second or third year due to the significantly greater following the tournament has in Canada compared to other participating countries. Originally, Switzerland was selected to host the WJHC in 2010, but withdrew. Buffalo, New York, in the United States, hosted the tournament in 2011 and 2018; in both cases, proximity to Canada's population core in Southern Ontario was a key factor in the city winning the bidding rights.

The tournament offers one of the most prestigious stages for young hockey players, significantly boosting a player's value for upcoming NHL Entry Drafts.

Punch-up in Piestany

One of the most infamous incidents in WJC history occurred in 1987 in Piestany, Czechoslovakia (now part of Slovakia), where a bench-clearing brawl occurred between Canada and the Soviet Union. It began when the Soviet Union's Pavel Kostichkin took a two-handed slash at Canadian player Theoren Fleury. The Soviet Union's Evgeny Davydov then came off the bench, eventually leading to both benches emptying. The officials, unable to break up the numerous fights, left the ice and eventually tried shutting off the arena lights, but the brawl lasted for 20 minutes before the IIHF declared the game null and void. A 35-minute emergency meeting was held, resulting in the delegates voting 7–1 (the sole dissenter was Canadian Dennis McDonald) to eject both teams from the tournament. The Canadian team chose to leave rather than stay for the end-of-tournament dinner, from which the Soviet team was banned.

While the Soviets were out of medal contention, Canada was playing for the gold medal and was leading 4–2 at the time of the brawl. The gold medal ultimately went to Finland, hosts Czechoslovakia took the silver and Sweden, who had previously been eliminated from medal contention, was awarded the bronze.