The Spanish 2009–10 Tercera División started on 29 August 2009 and ended on 20 June 2010 with the promotion play-off finals.
There were 362 clubs competing in Tercera División (Third division) in the 2009–10 season, divided into 18 regional groups, accommodating between 20 and 22 clubs.
The following clubs finished as champions of their respective groups
The 18 group champion clubs participated in the Group Winners Promotion Play-off and the losers from these 9 play-off ties then proceeded to the Non-champions Promotion Play-off with clubs finishing second third and fourth.
Promoted to Segunda División B: Deportivo B, Gandía, Atlético Baleares, Alcalá, Real Sociedad B, Teruel, Badajoz, Caudal and Rayo B.
Promoted to Segunda División B: Getafe B, Yeclano, Coruxo, Santboià, La Muela, Alzira, Peña Sport, Extremadura and L'Hospitalet.