The Segunda Division B is the third highest division of Spanish football and is administered by the RFEF. It was founded in 1928-1929 and initially comprised of 10 teams.
During the 1929-1930 season, the Segunda Division B was replaced by the Tercera Division and was revived only in 1977.
Currently the Segunda Division B comprises of 80 teams divided into four groups of 20. From the 2008-09 season, the four group winners will have the opportunity to be promoted directly and be name the overall Segunda División B champion. The four group winners will be drawn into a two-legged series where the two winners will be promoted to the Liga Adelante (or the Segunda Division in Spain) and enter into the final for the Segunda División B champion. The two losing semifinalists enter the playoff round for the last two promotion spots.
The four group runners-up will be drawn against one of the three fourth-placed teams outside their group while the four third-placed teams are drawn against one another in a two-legged series. The six winners advance with the two losing semifinalists to determine the four teams that will enter the last two-legged series for the last two promotion spots.
In all the playoff series, the lower-ranked club plays at home first. Whenever the is a tie in position, a draw will determine the club to play at home first.
The four 16th-placed teams enter into a relegation playoff to determine the two teams to be relegated. One team is paired with one of the others in home and away series. the two winners remain in the division while the losers are relegated.