This volume of Lecture Notes in Computer Science contains the revised versions of the papers presented at the 9th International Conference on Implemen- tion and Application of Automata, CIAA 2004. Also included are the extended abstracts of the posters accepted to the conference. The conference was held at Queen s University in Kingston, Ontario, Canada on July 22 24, 2004. As for its predecessors, the theme of CIAA 2004 was the implementation of automata and grammars of all types and their application in other ?elds. The topics of the papers presented at the conference range from...