High Speed 1 (HS1), officially known as the Channel Tunnel Rail Link (CTRL) and originally as the Union Railway or Continental Main Line (CML), is a 108-kilometre (67 mi) high-speed railway from London through Kent to the British end of the Channel Tunnel.

The line was built to carry international passenger traffic from the United Kingdom to Continental Europe; additionally it carries domestic passenger traffic to and from towns and cities in Kent, and has the potential to carry Berne gauge freight traffic. The line, crossing over the River Medway and underneath the River Thames to London St Pancras railway station, opened in full on 14 November 2007. It allows speeds of 230 to 300 kilometres per hour (143 to 186 mph) and cost £5.8 billion to build. There are intermediate stations at Stratford International, Ebbsfleet International and Ashford International.

International passenger services are currently provided by Eurostar, with journey times of London St Pancras to Paris Gare du Nord in 2 hours 15 minutes, and St Pancras to Brussels-South in 1 hour 51 minutes, using a fleet of 27 Class 373/1 multi-system trains capable of 300 kilometres per hour (186 mph). Other, competing, passenger operators are expected to use the line in future.

High Speed or high-speed may refer to items in the following categories: