The Bannan or Blue line (code BL) is a metro line of Taipei Metro in Taipei, Taiwan, with a total of 23 stations serving the districts of Nangang, Xinyi, Daan, Zhongshan, Wanhua, Banqiao and Tucheng.

The line's name is a portmanteau of Banqiao and Nangang.

The excavation of tunnels using the cut-and-cover method resulted in large scale detouring of road traffic.

Because of that, the line runs beneath existing roads and totals 28.3 km (17.6 mi).

Due to Taipei City Hall being at the centre of the Taipei 101 New Year's festivities, intervals between trains can be reduced to a minimum of 135 seconds, transporting up to 39,000 passengers per hour.