The Blue Line is a metro rail line of the Delhi Metro, a rapid transit system in Delhi, India.Mostly elevated, it is the longest line of the network and consists of a Main Line (Line 3) with 50 stations from Noida Electronic City to Dwarka Sector 21, with a length of 56.11 kilometres and a Branch Line (Line 4) consisting of 8 stations from Vaishali to Yamuna Bank, with a length of 8.51 kilometres.

The Delhi Metro is a mass rapid transit system which serves Delhi and its adjoining satellite cities, such as Ghaziabad, Faridabad, Gurugram, Noida and Bahadurgarh, in the National Capital Region of India. The system consists of 10 colour-coded lines serving 256 stations, with a total length of 350.42 kilometres (217.74 mi). It is India's largest and busiest metro rail system and the second-oldest, after the Kolkata Metro. The metro has a mix of underground, at-grade, and elevated stations using broad-gauge and standard-gauge tracks. The metro makes over 4,300 trips daily.