Hedwig’s Theme: magical mood cast by the celesta melody

Hedwig's Theme, also known as the main theme of all eight Harry Potter films, was the first piece written by John Williams for the franchise to give Warner Bros and director Chris Columbus an idea of what this magical concept would grow into. 

Starting with a song-like solo melody, Hedwig's Theme immediately grabs the listener's attention, setting a rather mysterious mood, not in the least thanks to the use of the celesta—a keyboard instrument that rarely appears in either classical or popular music.

In its shape and design, the celesta is very similar to the piano, with the only difference being the sound extraction process. Here it's produced by the hammers striking metal plates rather than strings. That is why the tunes performed on celesta are so reminiscent of the sound of bells, and the instrument itself is sometimes referred to as bell-piano.

Listen to Hedwig's Theme by John Williams:

John Williams was not the first to notice the child-like nature of the celesta as the instrument had already appeared in soundtracks for the 1940 animated musical fantasy Pinocchio and 1971 film Willy Wonka & the Chocolate Factory.