This volume contains the refereed proceedings of the 13th International Conference on Logic Programming and Nonmonotonic Reasoning, LPNMR 2015, held in September 2015 in Lexington, KY, USA.

Invited Talk: Stable Models for Temporal Theories.- Invited Talk: Algorithmic Decision Theory meets Logic.- Invited Talk: Relational and Semantic Data Mining.- Shift-design with Answer Set Programming.- Advances in WASP.- Improving Coordinated SMT-based System Synthesis by Utilizing Domain-specific Heuristics.- Integrating ASP into ROS for Reasoning in Robots.- Automated inference of rules with exception from past legal cases using ASP.- Online Action Language oBC+.-aspartame: Solving Constraint Satisfaction Problems with Answer Set Programming.- _Add Another Blue Stack of the Same Height!_: Plan Failure Analysis and Interactive Planning Through Natural Language Communication.- A Theory of Intentions for Intelligent Agents (Extended Abstract).- Answer Set Programming modulo Acyclicity.- A Framework for Goal-Directed Query Evaluation with Negation.- Implementing preferences with aspirin.- Diagnosing Automatic Whitelisting for Dynamic Remarketing Ads Using Hybrid ASP.- Performance Tuning in Answer Set Programming.- Enablers and Inhibitors in Causal Justifications of Logic Programs.- Efficient Problem Solving on Tree Decompositions using Binary Decision Diagrams.- Knowledge Acquisition via Non-Monotonic Reasoning in Distributed Heterogeneous Environments.- Digital Forensics Evidence Analysis: An Answer Set Programming.- Approach for Generating Investigation Hypotheses.- A Formal Theory of Justifications.- A New Computational Logic Approach to Reason with Conditionals.- Interactive debugging of non-ground ASP programs.- Linking Open-world Knowledge Bases using Nonmonotonic Rules.- ASP, Amalgamation, and the Conceptual Blending Workflow.- Diagnostic Reasoning for Robotics using Action Languages.- OOASP: Connecting Object-oriented and Logic Programming.- Reasoning with Forest Logic Programs Using Fully Enriched Automata.- ASP Solving for Expanding Universes.- Progress in clasp series 3.- Combining Heuristics for Configuration Problems Using Answer Set Programming.- Infinitary Equilibrium Logic and Strong Equivalence.- On the Relationship between Two Modular Action Languages: A Translation from MAD into ALM.- Compacting Boolean Formulae for Inference in Probabilistic Logic Programming.- Multi-Level Algorithm Selection for ASP.- Clause-Learning For Modular Systems.- Solving disjunctive fuzzy answer set programs.- Characterizing and Explaining Inconsistency in Logic Programs.- An Implementation of Consistency-Based Multi-Agent Belief Change using ASP.- ASPMT(QS): Non-monotonic spatial reasoning with Answer Set Programming Modulo Theories.- Mobile Robot Planning using Action Language BC with an Abstraction Hierarchy.- Logic Programming with Graded Modality.-The Design of the Sixth Answer Set Programming Competition.- Doctoral Consortium Extended Abstract: Planning With Concurrent Transaction Logic.- Doctoral Consortium Extended Abstract: Multi-context Systems with Preferences.- Doctoral Consortium Extended Abstract: Default Mappings in Ontology-Based DataAccess.- Doctoral Consortium Extended Abstract: Nonmonotonic Qualitative Spatial Reasoning.