This book constitutes the refereed proceedings of the 9th International Conference on Discovery Science, DS 2006, held in Barcelona, Spain in October 2006, co-located with the 17th International Conference on Algorithmic Learning Theory, ALT 2006.

The 23 revised long papers and the 18 revised regular papers presented together with 5 invited papers were carefully reviewed and selected from 87 submissions. The papers cover all issues in the area of automating scientific discovery or working on tools for supporting the human process of discovery in science. They address theoretical and methodological topics such as intelligent data analysis, knowledge discovery and machine learning, as well as their application to scientific knowledge discovery.