The ongoing success of the Intelligent Data Engineering and Automated Lea- ing (IDEAL) conference series re?ects the continuing need for intelligent - proaches to understanding relationships in the massive data sets which confront the modern researcher. FromitsoriginsinHongKongin1998, this focusupon thenatureofthe data hasbeenthe unifyingtheme oftheconference, allowingittobecomeakeyforum forresearcherstopresentnovelapproachestodataengineeringandlearning, and to provide a particularly valuable opportunity for cross-disciplinary exchange of ideasinemergingapplicationareas.Thisbreadthandcontinualevolutionmaybe seen in this year's programme, with sessions devoted to data mining and kno- edge engineering, bioinformatics, agent technologies and ?nancial engineering, together with the traditional focus on learning algorithms and systems. This volume in the Lecture Notes in Computer Science series contains - cepted papers presented at IDEAL 2005, held in Brisbane, Australia, during July 6-8, 2005. The conference received 167 submissions from throughout the world, which were subsequently refereed by the Programme Committee and - ditional reviewers. The vast majority of submissions received three independent reviews, and for some borderline submissions an additional, fourth review was commissioned prior to the decision being made. In the end, 76 papers were judged to be of su?cient quality for acceptance and inclusion in the proceedings, with a smaller set of these articles to be c- sidered for inclusion in planned special issues of a number of major journals - continuing a practice from recent IDEAL conferences. At the time of writing, this arrangement had been con?rmed with the International Journal of Neural Systems, and discussions were well advanced with two other publications.