The 1984–85 Segunda División B season was the 8th since its establishment.
40 teams joined the league, including four relegated from the 1983–84 Segunda División and 6 promoted from the 1983–84 Tercera División.
The composition of the groups was determined by the Royal Spanish Football Federation, attending to geographical criteria.
Teams from Andorra, Aragon, Asturias, Basque Country, Castile and León, Catalonia, Galicia and Navarre.
Teams from Andalusia, Balearic Islands, Castilla–La Mancha, Catalonia, Ceuta, Extremadura, Madrid and Valencian Community.