This book includes revised selected papers from the International Workshops on AI Approaches to the Complexity of Legal Systems, AICOL-XI@JURIX2018, held in Groningen, The Netherlands, on December 12, 2018; AICOL-XII@JURIX 2020, held in Brno, Czechia, on December 9, 2020; XAILA@JURIX 2020, held in in Brno, Czechia, on December 9, 2020. The 17 full and 4 short papers included in this volume were carefully reviewed and selected form 39 submissions. They represent a comprehensive picture of the state of the art in legal informatics. The papers are logically organized in 5 blocks: ¿Knowledge Representation; Logic, rules, and reasoning; Explainable AI in Law and Ethics; Law as Web