This volume contains the papers selected for presentation at the 1st Conference onModelingDecisionsforArti?cialIntelligence(MDAI2004),heldinBarcelona, Catalonia, August 2-4, 2004. The aim of this conference was to provide a forum for researchers to discuss models for information fusion (aggregation operators) and decision, to examine computational methods and criteria for model selection and determination, and to stimulate their application in new contexts. Fifty-three papers were submitted to the conference, from 19 di?erent co- tries. Each submitted paper was reviewed by at least two experts on the basis of technical soundness, originality, signi?cance and clarity. Based on the review reports, 26 papers were accepted for publication in this volume. Additionally, this volume contains the plenary talks given at the conference. We would like to express our gratitude to the members of the program c- mittee as well as to all reviewers for their work. We thank Alfred Hofmann, from Springer-Verlag,who supported the publication of these proceedings in the LNAI series. The conference was supported by the Catalan Association for Arti?cial Intelligence (ACIA), the European Society for Fuzzy Logic and Technology (EUSFLAT), the Japan Society for Fuzzy Theory and Intelligent Informatics (SOFT), the IEEESpanish Chapter,the Spanish Council for Scienti?
c Research (CSIC) and the Generalitat de Catalunya (AGAUR 2002XT 00111).