The tournament format (not including the play-in game) consists of four subsets known as regions, each of which contains 16 teams that are seeded number 1 to number 16 by the selection committee and then matched up according to seed, with the number 1 seed playing number 16, number 2 playing number 15, and so on. (The selection committee generally comprises university athletic directors and conference commissioners.) The first- and second-round games take place during the first week of the tournament at eight geographically dispersed sites, and the 16 teams that move on to the second week (having won both their first- and second-round games) are referred to as the “Sweet Sixteen.” These remaining teams then proceed to four regional sites and are further winnowed to an “Elite Eight” and a “Final Four,” the last of which advances to yet another location for the national semifinals and finals in the third week of the competion. The sizable field often produces pairings of large schools from highly regarded conferences with smaller automatic qualifiers that may result in first-round upsets, which can then lead to underdog teams (known as “Cinderellas”) advancing far in the tournament.

It is a common practice for fans to fill out tournament brackets with their predictions before the event begins and to enter their brackets into office pools (or on the Internet) with friends and coworkers. Studies have shown that American workers become less productive during March Madness, as large numbers of basketball fans frequently monitor the status of their brackets or discuss the tournament (or even watch the games) while on the job.