This book constitutes the proceedings of the 17th European Conference on Logics in Artificial Intelligence, JELIA 2021, held as a virtual event, in May 2021. The 27 full papers and 3 short papers included in this volume were carefully reviewed and selected from 68 submissions. The accepted papers span a number of areas within Logics in AI, including: argumentation; belief revision; reasoning about actions, causality, and change; constraint satisfaction; description logics and ontological reasoning; non-classical logics; and logic programming (answer set programming).

Graph-Classes of Argumentation Frameworks with Collective Attacks.- Introducing a Tool for Concurrent Argumentation.- Probabilistic Argumentation: an Approach Based on Conditional Probability - a Preliminary Report.- Conditional Descriptor Revision and its Implementation by a CSP.- Trust is All You Need: From Belief Revision to Information Revision.- Computing Defeasible Meta-Logic.- Syntax Splitting for Iterated Contractions, Ignorations, and Revisions Using Selection Strategies.- An Epistemic Logic for Multi-Agent Systems with Budget and Costs.- Epistemic Reasoning About Rationality and Bids in Auction.- Tractable Combinations of Theories via Sampling.- Analyzing Refutability of Difference Constraint Systems in Selected Refutation Systems.- Residuation for Lexicographic Orders.- Exploiting forwardness: Satisfiability and Query-Entailment in Forward Guarded Fragment.- An Algebraic View on p-Admissible Concrete Domains for Lightweight Description Logics.- ReAD: AD-Based Modular Ontology Classification.- Weighted Defeasible Knowledge Bases and a Multipreference Semantics for a Deep Neural Network Model.- A Computationally Grounded Logic of Graded Belief.- Tractability Frontiers in Probabilistic Team Semantics and Existential Second-Order Logic Over the Reals.- An Epistemic Probabilistic Logic With Conditional Probabilities.- On Syntactic Forgetting under Uniform Equivalence.- Solving a Multi-Resource Partial-Ordering Flexible Variant of the Job-Shop Scheduling Problem with Hybrid ASP.- Tractable Reasoning Using Logic Programs with Intensional Concepts.- Estimating Grounding Sizes of Logic Programs under Answer Set Semantics and System Predictor.- Testing in ASP: Revisited Language and Programming Environment.- An Abstract View on Optimizations in SAT and ASP.- Model Reconciliation in Logic Programs.- Lazy Stream Manipulation in Prolog via Backtracking: the Case of 2P-Kt.- Transforming Gringo Rules Into Formulas in a Natural Way.- DualGrounder: Lazy Instantiation via Clingo Multi-Shot Framework.- A Multi-shot ASP Encoding for the Aircraft Routing and Maintenance Planning Problem.