The Elizabeth line is a high-frequency hybrid commuter rail and rapid transit service in London and its suburbs. It runs services on dedicated infrastructure in central London between London Paddington and Abbey Wood; along the Great Western Main Line from London Paddington to Reading and Heathrow Airport in the west; and along the Great Eastern Main Line between Liverpool Street and Shenfield in the east. The service is named after Queen Elizabeth II, who officially opened the line on 17 May 2022 during her Platinum Jubilee year; passenger services started on 24 May 2022.

Under the project name of Crossrail, the system was approved in 2007, and construction began in 2009. Originally planned to open in 2018, the project was repeatedly delayed, including for several months as a result of the COVID-19 pandemic.

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Many of the stations were previously owned and managed by TfL Rail, so some are new stations and some are very old stations that have either been converted, redeveloped or demolished and rebuilt. 

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The main depots are in west London at Old Oak Common TMD, in south-east London at Plumstead Depot, and in east London at Ilford EMU Depot and at a new signalling centre at Romford in Havering, East London.

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When the line opened, it did so in three sections:

1. Reading to Paddington, with a branch from Hayes & Harlington to Heathrow.

2. Liverpool Street to Shenfield and

3. The new core section from Paddington to Abbey Wood, but Bond Street did not open at this time owing to complications with the construction. When the line opened, if you wanted to go from Abbey Wood to Reading, you would have to get off at Paddington underground and then go over the main concourse to pick up a service from one of the Mainline platforms as explained in this video by Geoff Marshall.

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The line serves 41 stations and is 73 miles long.