High-speed rail in Spain in the context of "Standard gauge"

High-speed rail (HSR) is a type of rail transport network utilizing trains that run significantly faster than those of traditional rail, using an integrated system of specialized rolling stock and dedicated tracks. While there is no single definition or standard that applies worldwide, lines built to handle speeds of at least 250 km/h (155 mph) or upgraded lines of at least 200 km/h (125 mph) are generally considered to be high-speed.

The first high-speed rail system, the Tōkaidō Shinkansen, began operations in Honshu, Japan, in 1964. Due to the streamlined spitzer-shaped nose cone of the trains, the system also became known by its English nickname bullet train. Japan's example was followed by several European countries, initially in Italy with the Direttissima line, followed shortly thereafter by France, Germany, and Spain. Today, much of Europe has an extensive network with numerous international connections. Construction since the 21st century has led to China taking a leading role in high-speed rail. As of 2023, China's HSR network accounted for over two-thirds of the world's total.

High-speed rail (HSR) has developed in Europe as an increasingly popular and efficient means of transport. The first high-speed rail lines on the continent, built in the late 20th century, improved travel times on intra-national corridors. Since then, several countries have built extensive high-speed networks, and there are now several cross-border high-speed rail links.

As of 2025, several European countries — among them France, Spain, Italy, Germany, Austria, Belgium, the Netherlands, and the United Kingdom — are connected to a cross-border high-speed railway network. Spain operates the largest high-speed rail network in Europe with 3,973 km (2,469 mi) and the second-largest in the world, trailing only China. High-speed rail in the region predominantly runs in Western Europe, with comparatively very few having been built in Eastern Europe.

A standard-gauge railway is a railway with a track gauge of 1,435 mm (4 ft 8+1⁄2 in). The standard gauge is also called Stephenson gauge (after George Stephenson), international gauge, UIC gauge, uniform gauge, normal gauge in Europe, and SGR in East Africa. It is the most widely used track gauge around the world, with about 55% of the lines in the world using it.

All high-speed rail lines use standard gauge except those in Russia, Finland, Uzbekistan, and some line sections in Spain. The distance between the inside edges of the heads of the rails is defined to be 1,435 mm except in the United States, Canada, and on some heritage British lines, where it is defined in U.S. customary/British Imperial units as exactly "four feet eight and one half inches", which is equivalent to 1,435.1 mm.