The French Baroque composer Marc-Antoine Charpentier (1643-1704) wrote a wide variety of works, including operas and a large amount of sacred music. His "Te Deum" is a motet, i.e. a choral work consisting of many movements, with its Prelude acting as an instrumental introduction written for a small ensemble. The Prelude is in rondo form and it is often played as a stand-alone piece, for example as a church voluntary. Its bright march-like nature makes it suitable for happy occasions such as weddings and other services. For this reason it is often played on an organ, and this arrangement for piano may also be played on an organ with or without pedals.
The work has also been adopted as the theme of the European Broadcasting Union, introducing its broadcasts and best known as the signature tune of the Eurovision Song Contest introducing the programme since the contest started in 1956. You can download the PDF sheet music, or mp3 and midi versions using the links in the left hand menu.