Thepapersinthisvolumewerepresentedatthe5thAsiaPaci?cWebConference (APWeb 2003), which was held in Xi'an, China during 23-25 April 2003. The World Wide Web has dramatically changed our ways of working, le- ning, entertaininganddoingbusinessinthelast10years. TheAsiaPaci?cregion has emerged in recent years as the fastest growing region in the world in the use of Web technologies as well as in making signi?cant contributions to WWW research and development. APWeb this year received 136 submissions from 21 countries and regions, including Australia, Belgium, Brazil, Canada, China, F- land, France, Germany, Greece, Hong Kong, Italy, Japan, Korea, Kuwait, New Zealand, Singapore, Switzerland, Taiwan, Turkey, UK, and USA. Each subm- sion was carefully reviewed by three members of the Program Committee. Only 39 regular papers and 16 short papers were accepted. While XML-related te- nologies continued to dominate at this year's APWeb conference, this volume - vealssomeemergingtrends, suchastheformalfoundationsofWebdatamana- ment, architectures and methodologies in Web information systems engineering, Web-based work?ow management systems, and the applications of data mining and distributed data management techniques in the new context of the Web. Also included in this volume are two high-quality papers from leading research groups on the topic of web mining (organized by Wen-Ying Ma of Microsoft - searchAsia). OnehighlightofAPWeb2003wasitshigh-pro?lekeynotespeakers, Marek Rusinkiewicz (Telcordia Technologies, USA), Minoru Etoh (NTT DoCoMo USA Labs) and Beng Chin Ooi (National University of Singapore). Two keynote papers are included here. The conference received ?nancial support from Microsoft, Netec and a n- ber of Xi'an software industry and government agencies.