Its formal designation is Line 4, and it is the first section to be opened of a proposed Yokohama Circular Railway (横浜環状鉄道, Yokohama Kanjō Tetsudō).

Construction began in 2001 and the new line started operating on 30 March 2008.

[2] It uses linear motor propulsion and a full journey takes approximately 21 minutes one way.

The Green Line is operated by 17 4-car 10000 series EMUs.

In 2018, it was announced that 10 of these would be lengthened to six cars each by 2024 as a measure to ease overcrowding on the Green Line.