The West Anglia Main Line is one of the two main lines that operate out of Liverpool Street, the other being the Great Eastern Main Line, which operates services to Ipswich and Norwich via Colchester. It runs generally north through Cheshunt, Broxbourne, Harlow, Bishop's Stortford and Audley End (near Saffron Walden) to Cambridge, with branches between serving Stratford, Hertford and Stansted Airport. The line runs along the boundary between Hertfordshire and Essex for much of its length.

In the early years, the line was the main route from London to Cambridge. Following the opening of the Cambridge Line between Hitchin and Cambridge, the West Anglia Main Line is now primarily a commuter route for stations between Cambridge and London. It was an important goods route for many years as the southern end of a route from coalfields in Yorkshire, and there are still freight trains which run occasionally to Harlow and Rye House Power Station, along with a Network Rail base at Broxbourne.

For details on the routes in the London area, refer to the Lea Valley Lines article.