Sketches of an Elephant: A Topos Theory Compendium - Johnstone, Peter T. (, Reader in the Foundations of Mathematics, University of Cambridge, Cambridge, UK)

Topos Theory is a subject that stands at the junction of geometry, mathematical logic and theoretical computer science, and it derives much of its power from the interplay of ideas drawn from these different areas. This compendium aims to present a comprehensive account of the main approaches and demonstrate the overall unity of the subject.