The first three Harry Potter films have scores which are composed by John Williams. He is regarded as one of the greatest film composers of all time.
The film introduces many leitmotifs. These are tunes which belong to characters or themes; when they appear you will hear their tune played. These themes include two themes for Voldemort, two themes for Hogwarts, a Diagon Alley theme, a Quidditch theme, a flying theme, two friendship themes, and the main theme ("Hedwig's Theme"). This main theme can be found in all eight of the main Harry Potter films as well as the spinoff film 'Fantastic Beasts and where to find them'.
Soundtrack to Harry Potter
Hedwig’s theme played by an orchestra at the proms:
The main theme is played on a celesta (looks like a piano but the hammers inside hit metal plates rather than strings)