The Madrid Metro is a metro

Rapid transit

A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

 system serving the city of Madrid

Madrid

Madrid is the capital and largest city of Spain. The population of the city is roughly 3.3 million and the entire population of the Madrid metropolitan area is calculated to be 6.271 million. It is the third largest city in the European Union, after London and Berlin, and its metropolitan...

, capital of Spain

Spain

Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

. The system is the sixth longest metro in the world though Madrid is approximately the fiftieth most populous metropolitan area in the world. Its fast growth in the last 20 years has also put it among the fastest growing networks in the world, rivaled by many Asian metros such as the Delhi Metro

Delhi Metro

Delhi Metro is a rapid transit system serving Delhi, Gurgaon, Noida and Ghaziabad in the National Capital Region of India. It is one of the largest metro networks in the world. The network consists of six lines with a total length of with 142 stations of which 35 are underground...

, Shanghai Metro

Shanghai Metro

The Shanghai Metro is the urban rapid transit system of China's largest city, Shanghai. The system incorporates both subway and light rail lines. It opened in 1995, making Shanghai the third city in Mainland China, after Beijing and Tianjin, to have a rapid transit system...

, Guangzhou Metro

Guangzhou Metro

Guangzhou Metro is the metro system of the city of Guangzhou in Guangdong Province of China. It is operated by the state-owned Guangzhou Metro Corporation and was the fourth metro system to be built in mainland China, after those of Beijing, Tianjin and Shanghai.The earliest effort of preparation...

 or the Beijing Subway

Beijing Subway

The Beijing Subway is a rapid transit rail network that serves the urban and suburban districts of Beijing municipality. It is owned by the city of Beijing and has two operators, the wholly state owned Beijing Mass Transit Railway Operation Corp., which operates 12 lines, and the Beijing MTR...

. Unlike normal Spanish road and rail traffic, Madrid Metro trains use left-hand running on all lines due to historical reasons.

A light rail

Light rail

Light rail or light rail transit is a form of urban rail public transportation that generally has a lower capacity and lower speed than heavy rail and metro systems, but higher capacity and higher speed than traditional street-running tram systems...

 system feeding the metro opened in 2007 called Metro Ligero (light metro).
The first line of the Madrid metro opened on 17 October 1919 under the direction of the Compañía de Metro Alfonso XIII, with 8 stations and 3.5 km (2.2 mi).