Referred by the locals as “el Metro”, the lines of the Barcelona subway system run by TMB are 8, each of them with a number and a color assigned. Locals use the number to call each line, although lines 1 to 5 are also often called by their color. There’s a total of 165 stations, most of them inside Barcelona city, but some other in nearby suburbs as well. You can find updated TMB maps here.

L1 (red line)

Number of stations: 30 stops, along 20.7km / 12.8mi
End stations: Hospital de Bellvitge and Fondo (connecting the cities of L’Hospitalet de Llobregat and Santa Coloma de Gramenet through Barcelona). 
Use it to get to: Plaça Catalunya (city center, bottom of Passeig de Gracia and top of La Rambla), Urquinaona (Palau de la Música Catalana), Espanya (Hill of Montjuic), Arc de Triomf (1888 World Fair, Ciutadella Park), Glories (Encants flea market).
Type of route: Double track, underground except for the section between Mercat Nou and Santa Eulalia. Semi-automatic trains with driver.
Future extensions: There’s a plan to extend this line to El Prat Estacio from Hospital de Bellvitge, and to Badalona Pompeu Fabra from Fondo.

L2 (purple or pink line)

Number of stations: 18 stops, along 13.1km / 8.1mi
End stations: Paral·lel and Badalona Pompeu Fabra (connecting Barcelona with Sant Adria del Besos and Badalona). 
Use it to get to: Paral·lel (connection with the Funicular of Montjuic, Sant Pau del Camp monastery), Sant Antoni (food market and hipster district), Universitat (city center), Passeig de Gracia, (2 blocks from Casa Batllo), Monumental (old bullring), Sagrada Familia (Gaudi’s church), Encants (flea market).
Type of route: Double track, completely underground. Semi-automatic trains with driver.
Future extensions: There’s a plan to extend the line from Sant Antoni towards Zona Franca, where a connection with the L9 track would allow the trains to continue to the airport. Extending the line from Badalon Pompeu Fabra to the Hospital of Can Ruti is also a possbility being discussed.

L3 (green line)

Number of stations: 26 stops, along 20.7km / 11.4mi
End stations: Zona Universitaria and Trinitat Nova (the entire itinerary runs within Barcelona city).
Use it to get to: Zona Universitaria (FC Barcelona Stadium), Palau Reial (Gaudi’s Dragon Gate), Sants Station (AVE train to Madrid and most suburban train lines), Espanya (Montjuic Hill and Magic Fountain), Paral·lel (Funicular to Montjuic and Monastery of Sant Pau del Camp), Drassanes (bottom of La Rambla, Columbus statue, Maritime Museum and Port Vell), Liceu (opera house, Boqueria Market, Palau Guell), Catalunya (city center), Passeig de Gracia (in front of Casa Batllo), Diagonal (one block from Casa Mila), Fontana (squares of the Gracia district and Casa Vicens), Lesseps and Vallcarca (closest stops to Park Guell), Mundet (Parc del Laberint)
Type of route: Double track, completely underground. Semi-automatic trains with driver.
Future extensions: There’s a project to connect it with Trinitat Vella in the North end, and take it outside of the city through the Southern suburbs all the way to Sant Feliu de Llobregat.

L4 (yellow line)

Number of stations: 22 stops, along 17.3km / 10.7mi
End stations: La Pau and Trinitat Nova (the entire itinerary runs within Barcelona city).
Use it to get to: El Maresme Forum (Blue Building and CCCIB), Poblenou, Ciutadella-Vila Olimpica (beaches), Jaume I (Gothic Quarter, Born district and Picasso Museum), Urquinaona (city center and Palau de la Musica), Passeig de Gracia (2 blocks from Casa Batllo).
Type of route: Double track, underground except for the section between Mercat Nou and Santa Eulalia. Semi-automatic trains with driver.
Future extensions: There’s a project to extend the line from La Pau to Sagrera with three more stations.

L5 (blue line)

Number of stations: 27 stops, along 18,9km / 11.7mi
End stations: Cornella Centre and Vall d’Hebron, connecting the suburb of Cornella de Llobregat with Barcelona via L’Hospitalet and Esplugues de Llobregat.
Use it to get to: Collblanc (FC Barcelona stadium), Sants Estacio (AVE train to Madrid and most suburban train lines), Diagonal (two blocks from Casa Mila), Sagrada Familia, Sant Pau | Dos de Maig (Hospital de Sant Pau).
Type of route: Double track, underground except for occasional openings near Can Boixeres station. Semi-automatic trains with driver.
Future extensions: There’s no plans to extend the line: it’s considered final.

L9

Number of stations: 9 stops on its Northern section (L9N) and , 15 stops in its Southern section (L9S), with a total of 11.7km / 7.2mi.
End stations: La Sagrera and Can Zam (L9S, connecting Barcelona and Santa Coloma de Gramenet), Zona Universitaria and Aeroport T1 (L9N, connecting Barcelona with the airport via l’Hospitalet and El Prat de Llobregat).
Use it to get to: Barcelona Airport, Fira and Europa | Fira (Trade Show and congress venues), all three on L9S.
Type of route: Double track, underground except for a section near Zona Franca. Fully automatic trains without a driver.
Future extensions: The connection between L9S and L9N is under construction and should be finished by 2029, going through Sarria, Lesseps and Guinardo.

L10

Number of stations: 6 stops on its Northern section (L10N) and , 11 stops in its Southern section (L10S), with a total of 11.1km / 6.8mi.
End stations: Collblanc and ZAL | Riu Vell (L10S, connecting Barcelona and L’Hospitalet de Llobregat), La Sagrera and Gorg (L9N, connecting Barcelona and Badalona).
Use it to get to: industrial district such as ZAL, Zona Franca and Ciutat de la Justicia.
Type of route: Double track, underground except for the section between Zona Franca and ZAL | Riu Vell which runs outdoors on top of a viaduct. Fully automatic trains without a driver.
Future extensions: The connection between L10S and L10N is under construction and should be finished by 2029, going through Sarria, Lesseps and Guinardo, sharing tracks with the L9.

L11

Number of stations: 5 stops over 2.3km / 1.4mi.
End stations: Trinitat Nova and Can Cuias, both within Barcelona city.
Use it to get to: You aren’t likely to need to access this part of the city if you are visiting Barcelona.
Type of route: Single track except at the Torre Baro | Vallbona station, completely underground. Fully automatic trains without a driver.
Future extensions: Despite the original plan of connecting it with other suburban train lines, the projects are so far stopped.