The First International Conference on Algorithmic Decision Theory had been organized by Francesca Rossi and Alexis Tsoukiàs and had been held on October 20 - 23, 2009 in Venice, Italy. It provided an interdisciplinary forum for uncertainty and robustness in decision making, preferences in reasoning and decision, decision-theoretic artificial intelligence, and learning and knowledge extraction. It was organized by the COST Action IC0602 and the EURO Working Group on Preferences. The proceedings have been published by Springer-Verlag as Volume 5783 of the Lecture Notes of Computer Science.