GNER White Rose train at King's Cross railway station

The East Coast Main Line (ECML) is a major railway line in the United Kingdom which links London to Aberdeen, via Stevenage, Peterborough, Grantham, Doncaster, York, Durham, Newcastle-upon-Tyne, Berwick-upon-Tweed, Dunbar, Edinburgh, Leuchars, Dundee and Arbroath.

The line's southern terminus is at Kings Cross station in London; the northern terminus is Aberdeen station. In addition to this, there are two branches; the first leaves the line after Doncaster station to serve Wakefield Westgate station and Leeds station, while the other connects Edinburgh to Glasgow via Carstairs Junction.

The line was originally built in piecemeal fashion by many small railway companies, but mergers and acquisitions led to only three companies controlling the route (north to south; the North British Railway, the North Eastern Railway and the Great Northern Railway). In 1860 the companies established the East Coast Joint Stock to run through services using common vehicles. In 1923 all three were grouped into the London and North Eastern Railway (LNER).

The ECML is widely regarded as the fastest railway line in the UK (excluding the Channel Tunnel Rail Link), with most of the line rated at 125 mph (200 km/h). The InterCity 225 trains which serve the line would be capable of 225 km/h (140 mph) in normal service if the signalling were to be upgraded to handle the increased speed of traffic. They have even operated at speeds of up to 260 km/h in test runs. The high speeds are possible because the line goes through the flatter eastern areas of Great Britain, such as Lincolnshire and Cambridgeshire which allow for a straight track. Most of the line is completely straight after Doncaster heading south. In contrast the West Coast Main Line has to traverse parts of the Peak District, the Trent Valley and the mountains of Cumbria, which means more bends, and a lower speed of 110 mph (178 km/h) (although this has been addressed in recent years by the introduction of Pendolino tilting trains).

The ECML has been the backdrop for a number of famous rail journeys and locomotives. The line was worked for many years by the famous steam locomotives "The Flying Scotsman", and "Mallard", the latter was officially declared the world's fastest steam locomotive on the Grantham - Peterborough stretch, a title it holds to this day. The steam locomotives disappeared in the early 1960s, being replaced by diesels, the most popular of these being the InterCity 125 or "HST" (High Speed Train), introduced in 1976.

In what was seen by many as a surprising action for a Conservative government, the ECML between London and Edinburgh (including the Leeds and Carstairs branches) was electrified in the late 1980s using state money. The Campaign for Rail Enhancement Aberdeen to Edinburgh (CREATE) is campaigning for the Edinburgh-Aberdeen section of the ECML to be electrified.