Introducing VALICO-UD, a linguistically annotated resource explicitly built for learner language research and Natural Language Processing tasks. This book aims at offering some insights to those interested in the computational side of learner language research. It describes the development and possible applications of VALICO-UD, a treebank including 2,234 learner sentences written by English, French, German, and Spanish native speakers, and 2,234 parallel, normalised sentences (target hypotheses), both annotated in Universal Dependencies (UD) formalism. The treebank comprises a gold standard section, featuring manually-corrected UD annotations and explicit error annotation, as well as a silver standard, automatically-annotated in UD and with implicit error annotation. Discover how to utilise VALICO-UD for computational investigation and enhance your language studies with this novel resource.