The 2021 NCAA Division I men's basketball tournament culminated the season and began on March 18 and concluded on April 5.

Three of the four new D-I members for this season are using existing on-campus facilities: The other D-I newcomer, Bellarmine, announced a multi-year deal with the Kentucky State Fair Board on November 2, 2020, to play home games at Freedom Hall, located at the Kentucky Exposition Center near Louisville Muhammad Ali International Airport.

It had planned to hold them at the ESPN Wide World of Sports Complex in Orlando within a protected "bubble" (the same site had recently hosted the remainder of the 2019–20 NBA season under similar circumstances), but The Athletic reported that there had been disagreements over health and COVID-19 testing protocols that had been mandated by ESPN Events (in accordance with recommendations by the CDC), which were stricter than those being adopted by conferences.

Source for additional stats categories For this list, an "upset" is defined as a win by a team seeded 7 or more spots below its defeated opponent.

This is more restrictive than the NCAA's official definition, in which a difference of 5 seed lines is sufficient to declare an "upset".