A total of 22 teams will contest the league, including 15 sides from the 2020–21 season, three relegated from the 2020–21 La Liga, and four promoted from the 2020–21 Segunda División B.
The first team to be relegated from La Liga were Eibar, after a 1–4 loss to Valencia on 16 May 2021, ending their seven-year stay in the top tier.
The second team to be relegated were Valladolid, following a 1–2 home defeat against Atlético Madrid on 22 May 2021, in their final game of the season, ending their three-year stay in the top tier.
The first team to be relegated from Segunda División were Albacete, following a 1–1 against Lugo on 18 May 2021, effectively ending their four-years stay in the second tier.
According to the progress of the pandemic, the capacity allowed each month was decided by the Government of Spain, in agreement with the Autonomous Communities.