| Es war einmal | |
|---|---|
| Fairy-tale opera by Alexander von Zemlinsky | |
 The composer in 1908 | |
| Librettist | Maximilian Singer |
| Language | German |
| Based on | Der var engang by Holger Drachmann |
| Premiere | 22 January 1900 |
Es war einmal (Once upon a time) is a fairy-tale opera in a prologue and three acts by the Austrian composer Alexander von Zemlinsky, composed during 1897-99. The libretto, an adaptation of Marie von Borch's German translation of the fairy-tale play Der var engang by the Danish author Holger Drachmann, was written by Maximilian Singer.