The Copenhagen Opera House (in Danish usually called Operaen, literally The opera) is the national opera house of Denmark, and among the most modern opera houses in the world. It is also one of the most expensive opera houses ever built with construction costs well over US$500 million. It is located on the island of Holmen in central Copenhagen.

The Copenhagen Opera House is a donation from the A.P. Møller and Chastine McKinney Møller Foundation to the Danish people.

The Opera is located in Copenhagen just opposite the main castle Amalienborg at the shore of the harbour. The opera house is built in alignment with Amalienborg and The Marble Church, so that if one stands in the main entrance of the Opera, one can see the Marble Church over the water along the road through Amalienborg.

The house is administered by the Royal Danish Theatre and is one of the best-equipped in the world. It has a main stage with five other stages directly connected, where large setups can be moved easily in and out.

It totals 41,000 square metres. Five of the fourteen storeys are subterranean. The main stage of the opera seats an audience of 1400.

The orchestra pit is one of the largest in any opera house, with room for 110 musicians; the structure provides excellent sound quality for the orchestra. If the pit is filled, some musicians are located just below the front of the stage, which has become controversial among some members of the orchestra (according to tour guides in 2005), because this increases the sound levels, beyond those acceptable in Denmark. However, the overhang is very slight and the authorities have permitted this to happen.

Guided tours cover most of the building, including both the auditorium and backstage areas.

The building was designed by architect Henning Larsen in close and often problematic collaboration with Mærsk Mc-Kinney Møller. Mærsk wanted the building to have several features in its design: it would not become obsolete in function and appearance due to any fiscal compromise. He personally tested seats and materials, he visited many places in the world to see how opera buildings were constructed and how the building materials were looking after having being exposed over time to weather. Henning Larsen, on the other hand, was trying to make sure that the original architectural ideas were carried through the construction process, especially concerning the large glass surface front, which became a matter of great controversy and subsequent compromise. A number of Danish artists have contributed to the decor, among them Per Kirkeby who has created four bronze reliefs, and Danish-Icelandic artist Olafur Eliasson who has contributed the three light sculptures for the foyer.