Originally operated by the independent Ferrocarril Metropolitano Transversal de Barcelona, it is today operated by Transports Metropolitans de Barcelona (TMB) and is part of the ATM fare-integrated main transport system.

[1] The line was created in 1926 as a means to join the rail stations the city had in the 1920s, and in preparation for the 1929 Universal Exposition.

These stations are architecturally homogenous, and as in the case of most metro lines in Barcelona, ornamentation is virtually absent from them.

Most of the line is underground, except for one short section, and at one point it shares tunnels with mainline tracks.

Most of the line is underground, except for a short section between Plaça de Sants and Santa Eulàlia stations.