Six Nations Under 20s Championship

The Six Nations Under 20s Championship is an international rugby union tournament for the under-20 men's teams of the national unions making up the Six Nations Championship and is organised under the same format.

Originally the tournament was in an under-21 format but changed after four editions to under-20s in 2008. England were the inaugural winners and they have gone on to be the tournament's most successful team, winning ten of the twenty-one titles up to 2025 (the 2020 competition having been abandoned during the Covid pandemic), while four of the six teams involved have won the competition at some point.

The tournament is played annually during February and March on the same weekends as the senior men's Six Nations. The competition retains from its senior equivalent the concepts of both the Grand Slam, Triple Crown and the Wooden Spoon.