This book constitutes the thoroughly refereed post-conference proceedings of the 6th International Conference on Large-Scale Scientific Computations, LSSC 2007, held in Sozopol, Bulgaria, in June 2007. The 81 revised full papers presented together with 5 invited papers were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on robust multilevel and hierarchical preconditioning methods; monte carlo: tools, applications, distributed computing; operator splittings, their application and realization; recent advances in methods and applications for large scale computations and optimization of coupled engineering problems; control systems; environmental modelling; computational grid and large-scale problems; application of metaheuristics to large-scale problems; and contributed talks.