The two-volume set LNCS 5544-5545 constitutes the refereed proceedings of the 9th International Conference on Computational Science, ICCS 2009, held in Baton Rouge, LA, USA in May 2008. The 60 revised papers of the main conference track presented together with the abstracts of 5 keynote talks and the 138 revised papers from 13 workshops were carefully reviewed and selected for inclusion in the three volumes. The general main track of ICSS 2009 was organized in about 20 parallel sessions addressing the following topics: e-Science Applications and Systems, Scheduling, Software Services and Tools, New Hardware and Its Applications, Computer Networks, Simulation of Complex Systems, Image Processing, Optimization Techniques, and Numerical Methods.