Real Sociedad B

The team's origin dates from 1952 when the Real Sociedad youth team were runners-up in the Copa del Rey Juvenil and the club's board sought to bridge the gap between the talented teenagers and the senior team: the concept of Real Sociedad de Fútbol Junior was introduced, but economic problems delayed its first official match until 1955, immediately after the youth team won the Copa Juvenil. After quickly gaining promotion to the third tier to become part of the national football pyramid, a name change was required to differentiate them from the senior team, and San Sebastián Club de Fútbol was chosen. They first reached the second division in 1959–60, and achieved a best ever classification in the category after finishing fifth two years later; however, as the main squad was relegated from La Liga, San Sebastián was ineligible for promotion, being relegated instead.

In 1980, Sanse was promoted to the newly created Segunda División B, remaining in that category for 17 consecutive seasons. Afterwards they fluctuated between the third and fourth tiers, reaching the promotion playoffs of the former in 1991 and 2006 but subsequently falling short. In 1992, a change in rules forced the team to change its name, and it was renamed Real Sociedad de Fútbol B. Liga de Fútbol Profesional's rules prohibit B clubs from having different names from their parent club, the exceptions being Real Madrid Castilla and Sevilla Atlético. Upon celebrating its 50-year anniversary in 2007, the team had used 486 players, preparing dozens to represent the first team including the vast majority of the squad that won the Spanish championship twice in succession (1980–81 and 1981–82).

A change in the club structure from 2016 meant that most Sanse players would be promoted from a new subsidiary, Real Sociedad C (previously known as Berio), who would play in Tercera División with under-20 graduates of the club's youth system. The Real Sociedad C team must play at least one division below Real Sociedad B.

In the 2017–18 season, the team finished third in Group 2. In 2020–21, Sanse won their group and gained promotion to the second division 59 years since their last appearance, after defeating Algeciras in the promotion play-off finals. On 22 May 2022, Sanse was relegated back to the third tier after only one season in the second tier.

Club names

• Real Sociedad de Fútbol Junior – (1955–57)
• San Sebastián Club de Fútbol – (1957–91)
• Real Sociedad de Fútbol "B" – (1991–92)
• Real Sociedad de Fútbol, S.A.D. "B" – (1992–)