A metro station or subway station is a railway station for a rapid transit system, which as a whole is usually called a Metro or Subway. The station provides a means for passengers to purchase tickets, access trains stopping at its platforms and evacuate the system in the case of an emergency.
Most stations are located underground, with entrances/exits leading up to ground or street level. The bulk of the station is typically positioned under land reserved for public thoroughfares or parks. Placing the station underground reduces the outside area occupied by the station, allowing vehicles and pedestrians to continue using the ground-level area in a similar way as before the station's construction. This is especially important where the station is serving high-density urban precincts, where ground-level spaces are already heavily utilised.
In other cases, a station may be elevated above a road, or at ground level depending on the level of the train tracks. The physical, visual and economic impact of the station and its operations will be greater. Planners will often take metro lines or parts of lines at or above ground where urban density decreases, extending the system further for less cost. Metros are most commonly used in urban cities, with great populations.  Alternatively, a preexisting railway land corridor is re-purposed for rapid transit.
At street level the logo of the metro company marks the entrances/exits of the station. Usually, signage shows the name of the station and describes the facilities of the station and the system it serves. Often there are several entrances for one station, saving pedestrians from needing to cross a street and reducing crowding.
A metro station typically provides ticket vending and ticket validating systems. The station is divided into an unpaid zone connected to the street, and a paid zone connected to the train platforms. The ticket barrier allows passengers with valid tickets to pass between these zones. The barrier may operated by staff or more typically with automated turnstiles or gates that open when a transit pass is scanned or detected. Some small metro systems dispense with paid zones and validate tickets with staff in the train carriages.
Access from the street to ticketing and the train platform is provided by stairs, concourses, escalators, elevators and tunnels. The station will be designed to minimise overcrowding and improve flow, sometimes by designating tunnels as one way. Permanent or temporary barriers may be used to manage crowds. Some metro stations have direct connections to important nearby buildings (see underground city).
Most jurisdictions mandate that people with disabilities must have unassisted use of the station. This is resolved with elevators, taking a number of people from street level to the unpaid ticketing area, and then from the paid area to the platform. In addition, there will be stringent requirements for emergencies, with backup lighting, emergency exits and alarm systems installed and maintained. Stations are a critical part of the evacuation route for passengers escaping from a disabled or troubled train.
Some metro stations are interchanges, serving to transfer passengers between lines or transport systems. The platforms may be multi-level. Transfer stations handle more passengers than regular stations, with additional connecting tunnels and larger concourses to reduce walking times and manage crowd flows.
In some stations, especially where trains are fully automated, the entire platform is screened from the track by a wall, typically of glass, with automatic platform-edge doors (PEDs). These open, like elevator doors, only when a train is stopped, and thus eliminate the hazard that a passenger will accidentally fall (or deliberately jump) onto the tracks and be run over or electrocuted.
Control over ventilation of the platform is also improved, allowing it to be heated or cooled without having to do the same for the tunnels. The doors add cost and complexity to the system, and trains may have to approach the station more slowly so they can stop in accurate alignment with them.
Metro stations, more so than railway and bus stations, often have a characteristic artistic design that can identify each stop. Some have sculptures or frescoes. For example, London's Baker Street station is adorned with tiles depicting Sherlock Holmes. The tunnel for Paris' Concorde station is decorated with tiles spelling the Déclaration des Droits de l'Homme et du Citoyen. Every metro station in Valencia, Spain has a different sculpture on the ticket-hall level. Each of the original four stations on Line 8 of the Beijing Subway is decorated traditionally with elements of Chinese culture. Alameda station is decorated with fragments of white tile, like the dominant style of the Ciutat de les Arts i les Ciències. On the Tyne and Wear Metro, the station at Newcastle United's home ground St James' Park is decorated in the clubs famous black and white stripes. Each station of the Red Line and Purple Line subway in Los Angeles was built with different artwork and decorating schemes, such as murals, tile artwork and sculptural benches. Every station of the Mexico City Metro is prominently identified by a unique icon in addition to its name, because the city had high illiteracy rates at the time the system was designed.
Some metro systems, such as those of Naples, Stockholm, Moscow, St. Petersburg, Tashkent, Kiev, Montreal, Lisbon, Kaohsiung and Prague are famous for their beautiful architecture and public art. The Paris Métro is famous for its art nouveau station entrances; while the Athens Metro is known for its display of archeological relics found during construction.
However, it is not always the case that metro designers strive to make all stations artistically unique. Sir Norman Foster's new system in Bilbao, Spain uses the same modern architecture at every station to make navigation easier for the passenger, though some may argue that this is at the expense of character.