Donkey Skin (French: Peau d'âne; also known in English as Once Upon a Time and The Magic Donkey) is a 1970 French musical fantasy romance comedy film directed by Jacques Demy, based on Donkeyskin, a 1695 fairy tale by Charles Perrault about a king who wishes to marry his own daughter.

Following the advice of her godmother, the lilac fairy, the princess demands a series of seemingly impossible nuptial gifts in the hope that her father will be forced to give up his plans of marriage.

However, the king succeeds in providing her with dresses the colour of the weather, the moon and the sun and finally with the skin of a magic donkey that excretes jewels, the source of his kingdom's wealth.

Love-struck, he retires to his sickbed, and asks that Donkey Skin be instructed to bake him a cake to restore him to health.

Jacques Demy, fascinated by Charles Perrault's fairy tale since childhood, was working on a script for the film as early as 1962.