2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/173976This is an introduction to the theory of decoherence with an emphasis on its microscopic origins and on a dynamic description. The text corresponds to a chapter soon to be published in: A. Buchleitner, C. Viviescas, and M. Tiersch (Eds.), Entanglement and Decoherence. Foundations and Modern Trends, Lecture Notes in Physics, Vol 768, Springer, Berlin (2009)57 pages, 2 figures; some new material added and typos corrected. This corresponds to the published versionQuantum Physicstext