The National Theatre in Oslo (Nationaltheatret) is one of Norway's largest and most prominent venues for performance of dramatic arts.

The theatre had its first performance on 1 September 1899 but can trace its origins to Christiania Theatre, which was founded in 1829. There were three official opening performances, on subsequent days in September: first, selected pieces by Ludvig Holberg, then An Enemy of the People by Henrik Ibsen, and on the third day Sigurd Jorsalfar by Bjørnstjerne Bjørnson.

The National Theatre was founded as a private institution and weathered several financial crises until 1929, when the Norwegian government started providing modest support. A number of famous Norwegians have served as artistic directors for the theatre, but Vilhelm Krag who took over in 1911, is credited as having brought the theatre into its "golden age."

The theatre is often considered the home for Ibsen's plays, and most of his works have been performed here. Notable is also the children's Christmas play, The Journey to the Christmas Star (Reisen til Julestjernen), written by the then theatre's finance director Sverre Brandt and performed for the first time in 1924.

The main building is centrally located between the Royal Palace, Oslo and the Parliament of Norway. It is served by National Theatre Station and National Theatre metro stations. It was designed by architect Henrik Bull. The theatre organisation manages four stages: the main stage (Hovedscenen), the amphitheatre (Amfiscenen) and Painting Parlour (Malersalen) within the main building. The fourth is the Torshov Theatre (Torshovteatret) in the Torshov district of Oslo. As of 2009, the theatre's artistic director was Hanne Tømta.