The main characters of The Sound of Music are members of an actual family, the Trapps, who successfully toured the world of music in choral concerts.

The first scene takes place at the Nonnberg Abbey in Austria in 1938. The nuns are singing their Morning Hymn, but the postulant Maria is not with them, for she is on the mountain-top enjoying the beauty of Nature ("The Sound of Music"). The nuns, and the Mother Abbess particularly, are considerably disturbed about her, since they are convinced she is not ready to enter upon a life dedicated solely to religion ("Maria"). The Mother Abbess confesses that there are many pleasures in life which she shares with Maria ("My Favourite Things"), but for Maria's sake she decides to send the postulant away to serve as temporary governess for the seven children of Captain Georg von Trapp, a retired Austrian Naval officer, and a widower.

Maria comes to this household and completely wins over the children's affection, particularly after she entertains them and allays their fears during a thunderstorm ("The Lonely Goatherd"). She teaches the children to love music, and especially to sing ("Do, Re, Me"). And she can be uniquely sympathetic to the oldest of the children, Liesl, when she gets involved in her first love affair, with the village boy, Rolf Gruber ("Sixteen Going on Seventeen").

The Captain brings from Vienna Elsa Schraeder, his fiancée, who prevails on him to give a huge party. After the children bid the guests good night ("So Long, Farewell"), Maria becomes suddenly aware that she has fallen in love with her employer. Horrified, she flees from the villa back to the Abbey, where the Mother Abbess encourages her to overcome any obstacle that may lie in the way of her happiness ("Climb Every Mountain"). Returning to the villa, she finds that the Captain and his fiancée have separated following a quarrel over Nazism. The romance of Maria and the Captain now develops rapidly, but then the Nazis invade Austria on the eve of World War II …………