The 2018 National Championship tournament teams include champions from 32 Division I conferences (which receive automatic bids), and 36 teams which are awarded at-large berths. These "at-large" teams are chosen by an NCAA selection committee in a nationally televised event on the Sunday preceding the First Four play-in games, currently held in Dayton, Ohio, and dubbed Selection Sunday, as detailed below. The 68 teams are divided into four regions and organized into a single elimination "bracket", which pre-determines, when a team wins a game, which team it will face next.
Each team is "seeded", or ranked, within its region from 1 to 16. After an initial four games between eight lower-ranked teams, the tournament occurs during the course of three weekends, at pre-selected neutral sites across the United States. Lower-ranked teams are placed in the bracket against higher ranked teams. Each weekend eliminates three quarters of the teams, from a round of 64, to a "Sweet Sixteen", and for the last weekend of the tournament, a Final Four. The Final Four is usually played during the first weekend of April. These four teams, one from each region (East, South, Midwest, and West), then compete in one centralized location for the national championship.