Integrated Circuit and System Design. Power and Timing Modeling Optimization and Simulation : 21st International Workshop PATMOS 2011 Madrid Spain September 26 29 2011. Proceedings This book constitutes the refereed proceedings of the 21st International Conference on Integrated Circuit and System Design PATMOS 2011 held in Madrid Spain in September 2011. The 34 revised full papers presented were carefully reviewed and selected from numerous submissions. The paper feature emerging challenges in methodologies and tools for the design of upcoming generations of integrated circuits and systems and focus especially on timing performance and power consumption as well as architectural aspects with particular emphasis on modeling design characterization analysis and optimization.