The Osaka Metro Tanimachi Line (谷町線, Tanimachi-sen) is a rapid transit line of Osaka Metro, running from Dainichi Station in Moriguchi to Yaominami Station in Yao through Osaka. Despite chronologically being the system's fourth line, its official name is Rapid Electric Tramway Line No. 2 (高速電気軌道第2号線), while the Osaka Municipal Transportation Bureau refers to it as Osaka City Rapid Railway Line No. 2 (大阪市高速鉄道第2号線), and in MLIT publications, it is written as Line No. 2 (Tanimachi Line) (2号線(谷町線)). On line maps, stations on the Tanimachi Line are indicated with the letter T.
The central part of the line runs underneath Tanimachi-suji, a broad north–south thoroughfare lined with prefectural government buildings and Buddhist temples. Its only above-ground segment is the vicinity of Yaominami Station. The line color on maps, station signs and train livery is tyrian purple (京紫, kyō-murasaki), derived from the kasaya robes worn by Buddhist monks.