The Primera Division de Mexico is the highest division in Mexican football. It is a professional league and is run competently.
The Primera Division was founded in 1943. It was the nation’s first professional league. In its early stages, the league had to struggle financially but the hosting of the 1970 FIFA World Cup led to the boom of the Mexican league.
The Primera Division is now divided into two tournaments per year: the aperture (opening) championship that runs from August to December) and the clausura (closing) championship that runs from January to May.
At the end of a season, after the apertura and clausura championships, one team is relegated to the next lower division, Primera División A, and one team from that division is promoted and replaces the relegated side.
The relegated team is determined by computing the points-per-game-played ratio for each team, considering all the games played by the team during the last three seasons. The team with the lower ratio is relegated.
For teams recently promoted, only the games played since their promotion are considered (two or four tournaments). The team promoted from Primera Division A is the winner of a two-leg match between the champions of the apertura and clausura tournaments of that division. If a team becomes the champion in both tournaments, it is automatically promoted.
The Primera Division currently comprises of 18 teams. The most successful club is Club Deportivo Guadalajara who have won 11 titles. The reigning champions are Santos Laguna.