The Tercera División currently features 361 teams divided into 18 regional groups, corresponding to the Autonomous communities of Spain (due to its huge size, Andalucia is divided into two different groups, East and West; Ceuta is allocated to West Andalusia, while Melilla is allocated to the East). Each Group is administered by a regional football federation. At the end of the season the first four teams in each group qualify for promotion play-offs to decide which teams are promoted to Segunda División B. The three teams finishing bottom of each group may be relegated to the Divisiones Regionales de Fútbol. However the number of teams relegated can vary. The eighteen group champions also qualify for the following season's Copa del Rey. However reserve teams are ineligible. Along with teams from Segunda División B, the remaining teams from the division compete in the Copa Federación.
Since the 2008-09 season, the eighteen group winners have the opportunity to promote directly to the Segunda División B. The 18 group winners are drawn into a two-legged series where the nine winners promote to the Segunda División B. The nine losing clubs enter the playoff round for the last nine promotion spots.
The 18 runners-up are drawn against one of the seventeen fourth-place clubs outside their group and the 18 third-placed clubs are drawn against one another in a two-legged series. The twenty-seven winners advance with the nine losing clubs from the champions' series to determine the 18 teams that enter the last two-legged series for the last nine promotion spots. In all the playoff series, the lower-ranked club plays at home first. Whenever there is a tie in position (like the group winners in the champions' series or the third-placed teams in the first round), a draw determines the club to play at home first.
During the inaugural La Liga season of 1928/29 a third level of teams known as Segunda División B was also organised. This division featured 10 teams and at the end of the season Cultural y Deportiva Leonesa were crowned champions. However the 1929/30 season saw the first of many reorganisations of the Spanish football league system and the Tercera Division was born. During it first season the division featured 33 teams divided into eight groups. The eight group winners qualified for a play-off and CD Castellón eventually beat Barakaldo CF 3-2 to be declared champions. The most significant reorganisation came at the start of the 1977/78 season with the revival of Segunda División B which replaced the Tercera División as the third level.