Stabilization of Model Categories by Mark Hovey Wesleyan University Suppose C is a (nice enough) model category, and G: C --> C is a left Quillen endofunctor of C. Think of C as the category of pointed topological spaces, and G as the suspension. Then we construct a new model category Sp(C,G), an embedding C --> Sp(C,G), and an extension of G to a Quillen EQUIVALENCE of Sp(C,G). Essentially, we have inverted the functor G, up to homotopy. When C is the category of pointed topological spaces and G is the suspension, we recover the Bousfield-Friedlander model category of spectra. The trouble with the Bousfield-Friedlander model category is that it is not symmetric monoidal, and we have the same problem with Sp(C,G). But there is also the same fix. Suppose C is a (nice enough) symmetric monoidal model category, K is a cofibrant object of C, and D is a (nice enough) C-model category. Think of C as pointed simplicial sets, D as a pointed simplicial model category, and K as the simplicial circle. Then we construct a model category Sp^Sigma(D,K), so that Sp^Sigma(C,K) is a symmetric monoidal model category, Sp^Sigma(D,K) is a Sp^Sigma(C,K)-model category, and smashing with K is a Quillen equivalence on Sp^Sigma(D,K). When C is pointed simplicial sets, and K is S^1, we get the symmetric spectra of Hovey-Shipley-Smith. The method used is the Bousfield localization technology of Hirschhorn, so the words "nice enough" mean "left proper cellular", though occasionally we also need to assume to domains of the generating cofibrations are cofibrant.