Zemlinsky’s fairy-tale opera ''Es war einmal'' had a very successful world premiere in 1900 and was staged several times afterwards until 1926. The opera was then forgotten for several decades and presented to a public again only in 1987 by the Danish Broadcast. The libretto was written by Maximilian Singer after the play ''Der var engang'' by the Danish poet Holger Drachmann. This edition follows the heavily rearranged world premiere version by Mahler.