rd This book reports the scientific proceedings of the 23 International Symposium on High Performance Computing Systems and Applications. HPCS 2009 was held at Queen's University at Kingston, June 14-17, 2009. The symposium was hosted by HPCVL in co-operation with Compute Canada. The symposium brought together over 150 scientists from many countries including Brazil, Canada, China, UK, Germany and the USA. As the proceedings demonstrate, their work addresses fundamental HPC-related issues, from programming, to archit- tures, to applications and, finally, to upcoming challenges for HPC. In addition to the scientific program, reported here, the conference was addressed by keynote speakers on various topics including: . Andy Bechtolsheim, Sun Microsystems and Arista. "The Road from Peta-FLop To Exa-FLop: Exploring How Technology Road-Maps over the Next Ten Years Will Enable us to Build a Sustained Exa-Flop Computer by 2020. " . Russ Boyd, Alexander McLeod Professor of Chemistry, Dalhousie University. "Computational Chemistry: History, Grand Challenges and Opportunities. " . André Bandrauck, Canada Research Chair, Computational Chemistry and Molecular Photonics, Université de Sherbrooke. "MAST-Molecular Attosecond Simulations and Theory. " . Wolfgang Gentzsch, DEISA Project. "The European e-Infrastructure DEISA for e-Science Grand Challenges. " . Cynthia McIntyre, Sr. V. P. USA Council on Competitiveness. "How HPC Will Improve Competitiveness in the US. " . Tony Noble, Queen's University, Director of SNOlab. "HPC and the Sudbury Neutrino Laboratory. " . Suzanne Fortier, President, Natural Sciences and Engineering Research Council of Canada. "HPC and the Natural Sciences and Engineering Research Council.