  Nonmonotonic logic is a complex, robust research field. Providing a survey of the subject is made difficult by the fact that there are many different foundational paradigms for formalizing nonmonotonic reasoning, and the relations between these paradigms is not simple. An adequate account of even a significant part of the field requires a something like a book-length treatment. A number of books are available, including  Łukaszewicz 1990,  Brewka 1991,  Besnard 1992,  Marek &amp; Truszczynski 1994,  Antoniou 1997,  Brewka et al. 1997,  Schlechta 1997,  Antonelli 2005,  Makinson 2005b,  and  Horty 2012.  Two collections are especially useful:  Ginsberg 1987  and  Gabbay et al. 1994.  The former is a useful source for readers interested in the early history of the subject, and has an excellent introduction. The handbook chapters in  Gabbay et al. 1994  provide overviews of important topics and approaches. My current recommendation for readers interested in a quick, readable introduction to the topic would be  Brewka et al. 1997  and self-selected chapters of  Gabbay et al. 1994. Some other sources include  Bochman 2004, Makinson 2005, Antoniou and Wang 2007, Bochman 2007,  and Schlechta 2007. We rely on these references for technical background, and will concentrate on intellectual motivation, basic ideas, and potential long-term signifgicance for logic.