AbstractThe basic technical point of this paper is that a pseudo-simplicial category can be produced from primitive data consisting of face functors and degeneracy functors, natural isomorphisms corresponding to the standard simplicial identities, and a small list of higher order commutativity conditions relating these isomorphisms. A similar machine exists for constructing contravariant pseudo-functors on Segal's category Γ. Thus, a monoidal category M gives rise canonically to a pseudo-simplicial category BM which enjoys many of the properties of a classifying space construction, while a symmetric monoidal category A determines a Γo category ΓoA which then can be used to directly construct a Γo-space Γo∗A and a spectrum Spt(A). These cons...