The Osaka Metro Yotsubashi Line is an underground rapid transit line in Osaka, Japan, operated by Osaka Metro. The line connects Umeda, Hommachi, Yotsubashi, Namba, Daikokuchō and Suminoe, and runs parallel to the Midōsuji Line from Daikokuchō to Nishi-Umeda. Despite being the system's second line to open, its official name is Rapid Electric Tramway Line No. 3 (高速電気軌道第3号線), while the Osaka Municipal Transportation Bureau refers to it as Osaka City Rapid Railway Line No. 3 (大阪市高速鉄道第3号線), and in Ministry of Land, Infrastructure and Transport publications, it is written as Line No. 3 . Station numbers are indicated by the letter Y.

The Osaka Metro is a major rapid transit system in the Osaka Metropolitan Area of Japan, operated by the Osaka Metro Company, Ltd. It serves the city of Osaka and the adjacent municipalities of Higashiosaka, Kadoma, Moriguchi, Sakai, Suita, and Yao. Osaka Metro forms an integral part of the extensive mass transit system of Greater Osaka, having 123 out of the 1,108 rail stations (2007) in the Osaka-Kobe-Kyoto region. In 2010, the greater Osaka region had 13 million rail passengers daily of which the Osaka Municipal Subway accounted for 2.29 million.