​This book constitutes revised selected papers from the refereed proceedings of the 20th International Conference of the Italian Association for Artificial Intelligence, AIxIA 2021, which was held virtually in December 2021.The 36 full papers included in this book were carefully reviewed and selected from 58 submissions;

-Planning and Strategies.-Task Allocation for Multi-Robot Task and Motion Planning: a case for Object Picking in Cluttered Workspaces.-A Sound (but Incomplete) Polynomial Translation from Discretised PDDL+ to Numeric Planning.-Enhancing Telepresence Robots with AI: Combining Services to Personalize and React.-Tafl-ES: Exploring Evolution Strategies for Asymmetrical Board Games.-Constraints, Argumentation, and Logic Programming.-Combining DCOP and MILP for Complex Local Optimization Problems.-Automated Design of Elevator Systems: Experimenting with Constraint-Based Approaches.-Modular logic argumentation in Arg-tuProlog.-Burden of Persuasion in Meta-Argumentation.-Knowledge Representation, Reasoning, and Learning.-Reasoning about Smart Contracts encoded in LTL.-A Combinatorial Approach to Weighted Model Counting in the Two Variable Fragment with Cardinality Constraints.-Option Discovery for Autonomous Generation of Symbolic Knowledge.