Finlandia, Op. 26, is a tone poem by the Finnish composer Jean Sibelius. It was written in 1899 and revised in 1900. The piece was composed for the Press Celebrations of 1899, a covert protest against increasing censorship from the Russian Empire, and was the last of seven pieces performed as an accompaniment to a tableau depicting episodes from Finnish history. The premiere was on 2 July 1900 in Helsinki with the Helsinki Philharmonic Society conducted by Robert Kajanus. A typical performance takes between 7½ and 9 minutes depending on how it is performed.

In order to avoid Russian censorship, Finlandia had to be performed under alternative names at various musical concerts. Titles under which the piece masqueraded were numerous and often confusing —famous examples include Happy Feelings at the awakening of Finnish Spring, and A Scandinavian Choral March. According to Finland's tourism website, "While Finland was still a Grand Duchy under Russia performances within the empire had to take place under the covert title of 'Impromptu'."

Most of the piece is taken up with rousing and turbulent music, evoking the national struggle of the Finnish people. Towards the end, a calm comes over the orchestra, and the serene and melodic Finlandia Hymn is heard. Often incorrectly cited as a traditional folk melody, the Hymn section is of Sibelius' own creation.

Although he initially composed it for orchestra, in 1900 Sibelius arranged the work for solo piano.

Sibelius later reworked the Finlandia Hymn into a stand-alone piece. This hymn, with words written in 1941 by Veikko Antero Koskenniemi, is one of the most important national songs of Finland. It has been repeatedly suggested to be the official national anthem of Finland. Today, during modern performances of the full-length Finlandia, a choir is sometimes involved, singing the Finnish lyrics with the hymn section.

With different words, it is also sung as a Christian hymn (I Sought The Lord, And Afterward I Knew; Be Still, My Soul, When Memory Fades, Hail, Festal Day, in Italian evangelical churches: Veglia al mattino), and was the national anthem of the short-lived African state of Biafra (Land of the Rising Sun). In Wales the tune is used for Lewis Valentine's patriotic hymn Gweddi Dros Gymru (A Prayer for Wales).