The four-volume set LNCS 3043-3046 constitutes the refereed proceedings of the International Conference on Computational Science and its Applications, ICCSA 2004, held in Assisi, Italy in May 2004.The four volumes present a total of 460 revised reviewed papers selected from numerous submissions. The proceedings spans the whole range of computational science from foundational issues in computer science and mathematics to advanced applications in virtually all sciences making use of computational techniques. The four volumes give a unique account of recent results in the area