In 2017-18, there were 351 men's teams and 349 women's teams in Division I college basketball (two military colleges only have men's teams) and each team begins every basketball season with one dream — winning the national championship. But before these teams can win the tourney, they must make the field of teams that are invited to the tournament. Only 68 men's teams and 64 women's teams are granted invitations to what's often called the Big Dance.
A selection committee that comprises different university athletic directors and conference commissioners chooses teams for both the men's and women's tournaments. Each tournament has its own committee. The selection committee meets between the Thursday and Sunday before the date picked for the tournament's first game. Its job is to figure out the teams deserving of an invitation. The decisions are announced on television during Selection Sunday.
Thirty-two teams receive an automatic invite to the tournament, which is their reward for winning their respective postseason conference tournaments. The remaining invites, 36 for men and 32 for women, are left in the hands of the selection committee. Of the teams left in the pool, certain teams are assured a spot in the tournament, others don't make the cut, and then there's a third group, called bubble teams, that could go either way.