Segunda División B (English: second division B) was the third tier of the Spanish football league system containing 102 teams divided into five groups, until it was replaced by the new structure in 2021.

This division featured 10 teams and at the end of the season Cultural Leonesa were crowned champions.

The RFEF approved the expansion of the league initially to five groups of 20 teams each and recommended its further division into 10 subgroups of 10 teams each for ease of schedule, only for the 2020–21 season, due to promotion from the Tercera División groups in the curtailed 2019–20 season being applied.

[1][2] An additional two teams were promoted after the 2020 Tercera División play-offs were called off and could not be replayed.

Since the 2008–09 season, the four group winners had the opportunity to be promoted directly and be named the overall Segunda División B champion.

The six winners advanced with the two losing semifinalists to determine the four teams that will enter the last two-legged series for the last two promotion spots.

The six winners advanced with the two losing semifinalists to determine the four teams that entered the last single-match series for the two remaining promotion spots.

The two semifinal winners get promoted to Segunda División and play the final to decide the season champions.