Line 9 is a completely automated line of the Barcelona Metro network that is currently under construction, with 24 stations open in Barcelona and El Prat de Llobregat, L'Hospitalet de Llobregat, Badalona and Santa Coloma de Gramenet suburbs, since December 2009. The line is currently disconnected in two branches, with a connecting part between the two yet to be built. The Aeroport T1 – Zona Universitària section is called L9 South, and the La Sagrera – Can Zam portion L9 North. Upon completion, it will be the longest underground metro line in Europe.

The Barcelona Metro is a network of rapid transit electrified railway lines that run mostly underground in central Barcelona and into the city's suburbs. It is part of the larger public transport system of Barcelona, the capital of Catalonia, Spain, with unified fares under the Autoritat del Transport Metropolità (ATM) scheme. As of 2014, the network is operated by two separate companies: Transports Metropolitans de Barcelona (TMB) and Ferrocarrils de la Generalitat de Catalunya (FGC). It is made up of 12 lines, combining the lines owned by the two companies. Two lines, L9 and L10, are being built at present, with both lines having different sections of each opened between 2009 and 2018. They are due to be fully completed in 2026. Three lines on the network have opened as automatic train operation/driverless vehicle systems since 2009: Line 11 being converted to driverless first, and then Lines 9 and 10, opening up driverless.