What is March Madness? The popular US basketball tournament explained

NCAA competition pits nation's top teams against each other in fierce annual competition that began in 1939

A March Madness 2023 game between the Charleston Cougars and the San Diego State Aztecs in Orlando, Florida. Getty / AFP

Across the US every March, the flowers bloom, the trees grow new leaves — and everyone is glued to their TV screens for March Madness, the annual college basketball tournament.

The tournament is run by the National Collegiate Athletic Association (NCAA) and pits the nation's top university basketball teams against each other in a fierce competition that has taken place almost every year since 1939.

The competition was cancelled in 2021 due to the Covid-19 pandemic, the only time in history it was not held.

The single-elimination tournament involves 68 teams that compete in seven rounds for the national championship, with the second-to-last round known as the Final Four, when only four teams are left.

How are the teams chosen?

There are two ways that a team can earn a bid for the tournament, according to the NCAA. The 32 Division I conferences all receive an automatic bid, which they each award to the team that wins the postseason conference tournament.

The second way is receiving an at-large bid, which goes to the highest-scoring eligible teams across different levels, meaning even schools without big, expensive athletic departments have a chance to play.

Once the field of 68 teams is finalised, they are assigned a seed and sorted into four regions, which determines their first-round matchups and their path to the championship, according to the NCAA.

UCLA's Abramo Canka shoots a layup under North Carolina-Asheville's Drew Pember during the second half in the first round of the NCAA men's basketball tournament on March 16, 2023, in Sacramento, California. Getty / AFP

The tournament is wildly popular and even those not normally interested in college sports participate.

The big draw for fans isn't necessarily free-throw strategies or hook shots, however — it's the brackets.

At the beginning of every tournament, fans fill out a bracket, picking the teams they think will win in each game as well as which team will be the ultimate champion.

The craze attracts tens of millions of Americans every year and major sport channels such as ESPN and Fox Sports host online bracket tournaments in which winners can win hundreds of thousands of dollars.

Why do they call it March Madness?

The most obvious answer is because it mostly takes place in March. This year's tournament kicked off on Tuesday with the First Four - four games between lower-ranking teams to determine the last four in - and will continue to the NCAA championship game April 3.

The term was coined during the first year of the tournament in 1939, when Illinois high school official Henry V Porter wrote in a piece for a local magazine that “a little March madness may complement and contribute to sanity and help keep society on an even keel".

The ensuing sanity, however, might have a lot to do with whether your teams do as well as you hope they will.

Brackets for the NCAA tournament, which features 68 college basketball teams. AP