This book constitutes the refereed proceedings of the 9th Asian Computing Science Conference, ASIAN 2004, dedicated to Jean-Louis Lassez on the occasion of his 60th birthday and held in Chiang Mai, Thailand in December 2004. The 17 revised full papers presented together with 3 keynote papers and 16 invited papers honouring Jean-Louis Lassez were carefully reviewed and selected from 75 submissions. The contributed papers are focusing on higher-level decision making, whereas the invited papers address a broader variety of topics in theoretical computer science.