The 2021 IIHF World U18 Championship was the 22nd such event hosted by the International Ice Hockey Federation.

The tournament was held from April 26 to May 6, 2021, in Frisco and Plano, United States.

Winning teams were reseeded for the semifinals in accordance with the following ranking:[6] GP = Games played; G = Goals; A = Assists; Pts = Points; +/− = Plus–minus; PIM = Penalties In MinutesSource: IIHF (minimum 40% team's total ice time) TOI = Time on ice (minutes:seconds); GA = Goals against; GAA = Goals against average; SA = Shots against; Sv% = Save percentage; SO = ShutoutsSource: IIHF Source: IIHF Source: IIHF All lower division tournaments were cancelled by the IIHF.

[1] The tournament was to be held in Spišská Nová Ves, Slovakia, from April 5 to 11, 2021.

[7] The tournament was to be held in Kockelscheuer, Luxembourg, from March 28 to April 3, 2021.