 Suppression of interference has featured in many papers since the beginning of quantum mechanics, such as Mott’s (1929) analysis of \(\alpha\)-particle tracks. The modern foundation of decoherence as a subject in its own right was laid by H.-D. Zeh in the early 1970s (Zeh 1970, 1973). Equally influential were the papers by W. Zurek from the early 1980s (Zurek 1981, 1982). Some of these earlier examples of decoherence (e.g., suppression of interference between left-handed and right-handed states of a molecule) are mathematically more accessible than more recent ones. A concise and readable introduction to the theory is provided by Zurek in Physics Today (1991). This article was followed by publication of several letters with Zurek’s replies (1993), which highlight controversial issues. More recent surveys are given in Zeh (2003a), Zurek (2003), and in the books by Giulini et al. (1996, second edition Joos et al. 2003), and by Schlosshauer (2007).