Algorithmic decision theory is a new interdisciplinary research area that aims to bring together researchers from di?erent ?elds such as decision theory, d- crete mathematics, theoretical computer science and arti?cial intelligence, in order to improve decision support in the presence of massive databases, com- natorial structures, partial and/or uncertain information and distributed, p- sibly interoperating, decision makers. Such problems arise in several real-world decision-making scenarios such as humanitarian logistics, epidemiology, risk assessment and management, e-government, electronic commerce, and rec- mender systems. In 2007, the EU-funded COST Action IC0602 on Algorithmic Decision T- ory was started, networking a number of researchers and research laboratories around Europe (and beyond). The COST Action IC0602 now gathers over 100 participants from more than 30 countries (including non-COST countries such as Australia, South Africa and the USA). For more details see www.algodec.org. Within the Action, and in cooperation with the EURO Working Group on Pr- erences,itwasdecidedtostartanewseriesofconferencesonalgorithmicdecision theory, the goal being to provide a forum for researchers interested in this area. This volume contains the papers presented at ADT 2009, the ?rst Inter- tional Conference on Algorithmic Decision Theory. The conference was held in SanServolo,a smallislandintheVenetianLagoon,onOctober20–23,2009.The programoftheconferenceincludedoralpresentations,posters,invitedtalks,and tutorials (for more information see www.adt2009.org).