La naissance d'Osiris, ou La fête Pamilie (The Birth of Osiris, or The Festival of Pamylia) is a one-act opera by Jean-Philippe Rameau, first performed on 12 October 1754 at Fontainebleau to celebrate the birth of the future King Louis XVI. The libretto is by Rameau's frequent collaborator Louis de Cahusac. Cahusac styled the work a ballet allégorique ("allegorical ballet"), but it is usually categorised as an acte de ballet. Its slender plot tells of Jupiter's announcement to a group of Egyptian shepherds of the birth of the god Osiris, who symbolises the baby prince. The piece may have started life as part of a larger work, Les beaux jours de l'Amour, an opéra-ballet Rameau and Cahusac planned but never completed for reasons which are still uncertain.