Topoi : the categorial analysis of logic The first of its kind this book presents a widely accessible exposition of topos theory aimed at the philosopher logician as well as the mathematician. It is suitable for individual study or use in class at the graduate level (it includes 500 exercises). It begins with a fully motivated introduction to category theory itself moving always from the particular example to the abstract concept. It then introduces the notion of elementary topos with a wide range of examples and goes on to develop its theory in depth and to elicit in detail its relationship to Kripkes intuitionistic semantics models of classical set theory and the conceptual framework of sheaf theory (``localization of truth). Of particular interest is a Dedekind cuts style construction of number systems in topoi leading to a model of the intuitionistic continuum in which a ``Dedekind real becomes represented as a ``continuously variable classical real number