This volume contains the papers presented at ADT 2009, the first International Conference on Algorithmic Decision Theory. The conference was held in San Servolo, a small island of the Venice lagoon, during October 20-23, 2009. The program of the conference included oral presentations, posters, invited talks, and tutorials.

Social Choice Theory.- A Complete Conclusion-Based Procedure for Judgment Aggregation.- A Geometric Approach to Paradoxes of Majority Voting in Abstract Aggregation Theory.- Manipulating Tournaments in Cup and Round Robin Competitions.- Iterated Majority Voting.- Committee Selection with a Weight Constraint Based on Lexicographic Rankings of Individuals.- The Effects of Noise and Manipulation on the Accuracy of Collective Decision Rules.- Subset Weight Maximization with Two Competing Agents.- The Complexity of Probabilistic Lobbying.- On the Complexity of Efficiency and Envy-Freeness in Fair Division of Indivisible Goods with Additive Preferences.- On Low-Envy Truthful Allocations.- On Multi-dimensional Envy-Free Mechanisms.- Stable Rankings in Collective Decision Making with Imprecise Information.- Finding Best k Policies.- Multiple Criteria Decision Analysis.- New Hybrid Recommender Approaches: An Application to Equity Funds Selection.- A Prescriptive Approach for Eliciting Imprecise Weight Statements in an MCDA Process.- Inverse Analysis from a Condorcet Robustness Denotation of Valued Outranking Relations.- Directional Decomposition of Multiattribute Utility Functions.- The Possible and the Necessary for Multiple Criteria Group Decision.- Preferences in an Open World.- Extending Argumentation to Make Good Decisions.- Building Consistent Pairwise Comparison Matrices over Abelian Linearly Ordered Groups.- Aggregating Interval Orders by Propositional Optimization.- Circular Representations of a Valued Preference Matrix.- Decision under Uncertainty.- The First Belief Dominance: A New Approach in Evidence Theory for Comparing Basic Belief Assignments.- Interpreting GUHA Data Mining Logic in Paraconsistent Fuzzy Logic Framework.- Insuring Risk-Averse Agents.- AdversarialRisk Analysis: Applications to Basic Counterterrorism Models.- Game Theory without Decision-Theoretic Paradoxes.- Ranking Methods Based on Dominance Measures Accounting for Imprecision.- Optimisation.- Optimizing the Hurwicz Criterion in Decision Trees with Imprecise Probabilities.- Axioms for a Class of Algorithms of Sequential Decision Making.- Algorithmic Aspects of Scenario-Based Multi-stage Decision Process Optimization.- Choquet Optimization Using GAI Networks for Multiagent/Multicriteria Decision-Making.- Compact Preference Representation in Stable Marriage Problems.- Neuroevolutionary Inventory Control in Multi-Echelon Systems.- Determining a Minimum Spanning Tree with Disjunctive Constraints.- Learning.- An Inductive Methodology for Data-Based Rules Building.- A Framework for Designing a Fuzzy Rule-Based Classifier.- Anytime Self-play Learning to Satisfy Functional Optimality Criteria.