Tambara functors

Abstract: We survey and extend the theory of Tambara functors. These are algebraic structures similar to Mackey functors, but with multiplicative norm maps as well as additive transfer maps, and a rule governing their interaction that is most easily formulated in an abstract categorical framework. Examples include Burnside rings, representation rings, and homotopy groups of equivariant E-infinity ring spectra in stable homotopy theory. Some other examples are related to Witt rings in the sense of Dress and Siebeneicher.