It connects Plaça Espanya, in the Sants-Montjuïc district of Barcelona to the metropolitan area municipalities of L'Hospitalet, Cornellà and Sant Boi.

Line 8 is underground for most of its length and links Plaça Espanya, in Barcelona proper, with Sant Boi in the Baix Llobregat.

Therefore, line 8 shares the tracks with many other FGC services that travel beyond Molí Nou-Ciutat Cooperativa.

An extension of the line further into central Barcelona, with a new station in Plaça Francesc Macià, has been discussed since May 1999.

[3] The line is also projected to extend further towards the Besós river, serving stations such as Joanic, Sagrada Familia and Glòries.