King's Cross St Pancras (also known as King's Cross & St Pancras International) is a London Underground station on Euston Road in the Borough of Camden, Central London. It serves King's Cross and St Pancras main line stations in fare zone 1, and is an interchange between six Underground lines. The station was one of the first to open on the network. As of 2021, it is the most used station on the network for passenger entrances and exits combined.

The station opened in 1863 as part of the Metropolitan Railway, subsequently catering for the Hammersmith & City and Circle lines. It was expanded in 1868 with the opening of the City Widened Lines, and the Northern and Piccadilly platforms opened in the early 20th century. During the 1930s and 1940s, the station was restructured and partially rebuilt to cater for expanded traffic. The Victoria line connection opened in 1968. The 1987 King's Cross fire that killed 31 people is one of the deadliest accidents to occur on the Underground and resulted in widespread safety improvements and changes throughout the network. The station was extensively rebuilt in the early 21st century to cater for Eurostar services that moved from Waterloo to St Pancras, reopening in 2007.

The King's Cross fire began at approximately 19:30 on 18 November 1987 at King's Cross St Pancras tube station, a major interchange on the London Underground. As well as the mainline railway stations above ground and subsurface platforms for the Metropolitan, Circle and Hammersmith & City lines, there were platforms deeper underground for the Northern, Piccadilly, and Victoria lines. The fire started under a wooden escalator serving the Piccadilly line and, at 19:45, erupted in a flashover into the underground ticket hall, killing 31 people and injuring 100.

A public inquiry was conducted from February to June 1988. Investigators reproduced the fire twice, once to determine whether grease under the escalator was ignitable, and the other to determine whether a computer simulation of the fire—which would have determined the cause of the flashover—was accurate. The inquiry determined that the fire had been started by a lit match being dropped onto the escalator. The fire seemed minor until it suddenly increased in intensity, and shot a violent, prolonged tongue of fire, and billowing smoke, up into the ticket hall. This sudden transition in intensity, and the spout of fire, was due to the previously unknown trench effect, discovered by the computer simulation of the fire, and confirmed in two scale model tests.

London Underground was strongly criticised for its attitude toward fires; staff were complacent because there had never been a fatal fire on the system, and had been given little or no training to deal with fires or evacuation. The report on the inquiry resulted in resignations of senior management in both London Underground and London Regional Transport and to the introduction of new fire safety regulations. Wooden escalators were gradually replaced with metal escalators on the Underground.