The Northern line is one of two commuter rail routes operated by Merseyrail and centred on Merseyside, England, the other being the Wirral line. The cross-city route runs from Hunts Cross in south Liverpool then branches in the north to terminate at Southport, Headbolt Lane and Ormskirk (Lancashire).

Merseyrail is a commuter rail network which serves Merseyside and adjacent areas of Cheshire and Lancashire. Merseyrail serves 69 stations, 67 of which it manages, across two lines – the Northern Line and the Wirral Line. The network uses 750 V DC third rail electrified lines having 75.0 miles (120.7 km) of routes, of which 6.5 miles (10.5 km) are underground. Since January 2023, Merseyrail commenced replacing its train fleet, withdrawing the Class 507 and 508 trains and introducing 53 new Class 777 trains. The network carried 25.5 million passengers in the 2022/2023 statistical period.