Abstract
This article presents the longitudinal trilingual corpus of young learners of Italian, German and English called LEONIDE. The corpus consists of L1, L2 and L3 learner texts. L1 texts were written in two languages of schooling (i.e. Italian and German), L2 texts in two languages learned as second languages (i.e. German and Italian), and L3 texts in an additional foreign language (i.e. English). All texts were collected from a group of lower secondary school pupils from the multilingual Italian province of South Tyrol whose development in all three languages was observed over a period of three years. Each text comes with rich metadata as well as manual and automatic annotations.