This book constitutes the refereed proceedings of the 9th International Work-Conference on Artificial Neural Networks, IWANN 2007, held in San Sebasti??n, Spain in June 2007.

The 145 revised full papers presented together with 3 invited lectures were carefully reviewed and selected from over 260 submissions. The papers are organized in thematic sections on theoretical concepts and neurocomputational formulations, inmproving models and learning procedures, self-organizing networks, kernel methods, evolutionary and genetic algorithms, evolutionary learning, fuzzy systems, neuroengineering and hardware implementations, data analysis, signal processing, speech processing, images processing, time series and prediction, robotics and planning motor control, power system applications, internet and web applications, biomedical applications, neural networks and other machine learning methods in cancer research, assistive technologies and e-health, as well as other applications.