The papers in this volume were selected for presentation at the Ninth Annual International Symposium on Algorithms and Computation (ISAAC¿98),heldonDecember14¿16,1998inTaejon, Korea. P- viousmeetingswereheldinTokyo(1990),Taipei(1991),Nagoya (1992),HongKong(1993),Beijing(1994),Cairns(1995),Osaka (1996),andSingapore(1997). The symposium was jointly sponsored by Korea Advanced - stitute of Science and Technology (KAIST) and Korea Information Science Society (KISS) to commemorate its 25th anniversary in - operationwithMinistryofInformationandCommunication, Korea InformationSocietyDevelopmentInstitute,andKoreaScienceand Engineering Foundation. Inresponsetothecallforpapers,102extendedabstractswere submitted from 21 countries. Each submitted paper was reported on byatleastfourprogramcommitteemembers,withtheassistance ofreferees,asindicatedbytherefereelistfoundintheseproce- ings. There were many more acceptable papers than there was space availableinthesymposiumschedule,andtheprogramcommittee¿s task was extremely di?cult. The 47 papers selected for presentation hadatotalof105authors,residentasfollows: Japan24,Germany 17,UnitedStateofAmerica15,Taiwan10,HongKongandKorea 6each, Spain5,SwitzerlandandAustralia4each, Austria, Canada, andFrance3each, ItalyandNetherlands2each,andGreece1. We thank all program