Union Station, also known as Pennsylvania Station and commonly called Penn Station, is a historic train station in Downtown Pittsburgh, Pennsylvania. It was one of several passenger rail stations that served Pittsburgh during the 20th century; others included the Pittsburgh & Lake Erie Railroad Station, the Baltimore and Ohio Station, and Wabash Pittsburgh Terminal, and it is the only surviving station in active use.

The historic station was designed by Chicago architect Daniel Burnham and built from 1898 to 1904. The station's rotunda was added to the National Register of Historic Places in 1973, followed by the entire building in 1976. In the 1980s, the Burnham station building was converted to apartment use, while Amtrak, the national passenger railroad, moved its operations to an annex on the building's east side.

The current station replaced the original Union Station which was destroyed in the Pittsburgh railroad strike of 1877.

Unlike many union stations built in the U.S. to serve the needs of more than one railroad, this facility served only the Pennsylvania Railroad and its subsidiary lines. Thus, Union Station is a misnomer, for that reason, it was renamed in 1912 to match other Pennsylvania Stations. Other major passenger rail carriers served travelers at other stations. For instance, the New York Central used the Pittsburgh & Lake Erie Railroad Station, the Wabash Railroad used Wabash Pittsburgh Terminal, and the Baltimore and Ohio Railroad used both their own Baltimore and Ohio Station and the Pittsburgh & Lake Erie station.

The station building was designed by Chicago architect Daniel Burnham and built between 1898 and 1904. The materials were a grayish-brown terra cotta that looked like brownstone, and brick. Though Burnham is regarded more as a planner and organizer rather than a designer of details, which were left to draftsmen like Peter Joseph Weber, the most extraordinary feature of the monumental train station is its rotunda with corner pavilions. At street level, the rotunda sheltered turning spaces for carriages beneath wide, low vaulted spaces that owed little to any historicist style. Above, the rotunda sheltered passengers in a spectacular waiting room. Burnham's firm completed more than a dozen projects in Pittsburgh, some on quite prominent sites. The rotunda is listed on the National Register of Historic Places. Service began at the station on October 12, 1901.

On January 3, 1954, the Pennsylvania Railroad announced a US$3,600,000 (equivalent to $41,635,741 in 2024) in expansion and renovation for the complex. Into the beginning of the 1970s, the station remained a major stop for several of the PRR's leading east–west trains: Broadway Limited (Chicago–New York), Manhattan Limited (Chicago–New York); Penn Texas (St. Louis–New York) and Spirit of St. Louis (St. Louis–New York).

By the late 1970s the Penn Central Corporation was accepting bids for the complex and it was purchased by the US General Services Administration. There were proposals in 1978 to make the structure into a federal office building, a new city hall, and a senior citizens apartment building. Amtrak proposed that the whole structure remain a train station and rail offices. In 1974, the County Council proposed having the station be the site of the then-planned David L. Lawrence Convention Center. The Buncher Development Company had an option to buy the property as late as 1984.

A $20 million restoration of Union Station began in 1986 to convert the office tower into apartments. It is now called the Pennsylvanian and opened to residents on May 23, 1988. The concourse, which is no longer open to the public, was transformed into a lobby for commercial spaces on the ground floor and the paint cleaned off the great central skylight. The rotunda is now closed to vehicular traffic; modern cars and trucks are too heavy for the brick road surface and risk caving in the roof to the parking garage below it.