Wikipedia - Liga TDP

The Liga TDP is Mexico's fourth tier in the Mexican League System. The Liga TDP is divided into 17 groups. For the 2009/2010 season, the format of the tournament has been reorganized to a home and away format, which all teams will play in their respective group. The 17 groups consist of teams which are eligible to play in the liguilla de ascenso for three promotion spots, teams which are affiliated with teams in the Liga MX, Liga de Expansión MX and Liga Premier, which are not eligible for promotion but will play that who the better filial team in a sixteen team filial playoff tournament for the entire season.