This book constitutes the refereed proceedings of the 9th International Symposium on Algorithms and Computation, ISAAC'98, held in Taejon, Korea, in December 1998.The 47 revised full papers presented were carefully reviewed and selected from a total of 102 submissions. The book is divided in topical sections on computational geometry, complexity, graph drawing, online algorithms and scheduling, CAD/CAM and graphics, graph algorithms, randomized algorithms, combinatorial problems, computational biology, approximation algorithms, and parallel and distributed algorithms.