Description:This book constitutes the thoroughly refereed post-proceedings of the Metainformatics Symposium, MIS 2004, held in Salzburg, Austria in September 2004.The 17 revised full papers presented were carefully reviewed and selected for inclusion in the book. The papers are devoted to finding useful abstractions, notations, analytical frameworks, formalisms, and systems that improve the understanding of the underlying structure of various disciplines and families of systems within computer science.