H. Dieter Zeh studied physics in Brunswick and Heidelberg, where he began work on theoretical nuclear physics. After a year of research at the California Institute of Technology, he moved to the University of California in San Diego to work on the synthesis of the heavy elements, before returning to the University of Heidelberg, where he later became professor of theoretical physics. His studies of collective motion in nuclei led him to address the quantum-to-classical transition in general, and in particular the quantum measurement problem, which is in turn related to many aspects of irreversibility (arrows of time). During this work, Zeh recognized and formulated the universal and unavoidable role of uncontrollable quantum entanglement, thus becoming a founder of the area now known as decoherence.