ThePaci?c-AsiaConferenceonKnowledgeDiscoveryandData Mining hasbeen held every year from 1997. PAKDD 2009, the 13th in the series, was held in Bangkok, Thailand during April 27-30, 2008. PAKDD is a major inter- tional conference in the areas of data mining (DM) and knowledge discovery in database (KDD). It provides an international forum for researchers and ind- try practitioners to share their new ideas, original research results and prac- cal development experiences from all KDD-related areas including data mining, data warehousing, machine learning, databases, statistics, knowledge acqui- tion and automatic scienti?c discovery, data visualization, causal induction and knowledge-based systems. ForPAKDD2009,wereceived338researchpapersfromvariouscountriesand regions in Asia, Australia, North America, South America, Europe, and Africa. Every submission was rigorously reviewed by at least three reviewers with a doubleblindprotocol.Theinitialresultswerediscussedamongthereviewersand ?nally judged by the ProgramCommittee Chairs. When there was a con?ict, an additionalreviewwasprovidedbytheProgramCommitteeChairs.TheProgram Committee members were deeply involved in the highly selective process. As a result, only 39 papers (approximately 11.5% of the 338 submitted papers) were accepted as regular papers, 73 papers (21.6% of them) were accepted as short papers.