This volume contains the proceedings of the 21st Australasian Computer Science Conference (ACSC98), held in Perth, Australia, 4th-6th February 1998, and hosted by the University of Western Australia, Curtin University of technology, Edith Cowan University, and Murdoch University. Of the eighty four papers submitted and reviewed, forty six were accepted for presentation at the conference; these are published here together with the 2 keynote addresses by Prof. Takeshi Tokuyama and Prof. Gopal Gupta, respectively. Among the largely Australian-based contributions are also papers from China, France, Hong Kong, Indonesia, Malaysia, The Netherlands, New Zealand, United Kingdom, and the United States. The best Australian PhD thesis completed in 1997 was also awarded at the conference and is included in this volume. Readers will find in these proceedings an up-to-date view of the research being conducted in Australasia in all aspects of Computer Science.