The Aarne-Thompson-Uther (ATU) Index
The international classification system for folktale types, developed by Antti Aarne (1910), expanded by Stith Thompson (1928, 1961), and revised by Hans-Jorg Uther (2004).
The Aarne-Thompson-Uther Index (ATU) is the standard international classification system for folktale plot types. It assigns numerical codes to recurring narrative patterns found across cultures, allowing folklorists to track how the same basic story appears in different traditions worldwide. The system was created by Finnish folklorist Antti Aarne in 1910 (*Verzeichnis der Marchentypen*, published in German). American folklorist Stith Thompson translated and significantly expanded it in 1928 and again in 1961. German folklorist Hans-Jorg Uther published a major revision in 2004 (*The Types of International Folktales*), adding more eastern and southern European tales and correcting imprecise descriptions. Examples of ATU numbers: ATU 333 = Little Red Riding Hood, ATU 123 = The Wolf and the Seven Little Goats, ATU 510A = Cinderella, ATU 440 = The Frog King. The system is organized into broad categories: Animal Tales (1–299), Ordinary Folktales (300–1199), Jokes and Anecdotes (1200–1999), and Formula Tales (2000–2399). Modern researchers like Phylogenetic Analysis of Fairy Tales have combined ATU classifications with phylogenetic methods to study how tales evolve and spread across cultures.