La sonnambula is an Italian opera in two acts by Vincenzo Bellini , first performed at La Scala in Milan , on March 6 , 1831 , libretto by Felice Romani , after EugÃ ne Sribe 's ballet-pantomime La somnanbule . La sonnambula ( The Sleepwalker ) is an opera semiseria in two acts , with music in the bel canto tradition by Vincenzo Bellini to an Italian libretto by Felice Romani , based on a ballet-pantomime by EugÃ ne Scribe .