This guide to the universe aims to provide a comprehensive account of our present understanding of the physical universe, and the essentials of its underlying mathematical theory. It attempts to convey an overall understanding--a feeling for the deep beauty and philosophical connotations of the subject, as well as of its intricate logical interconnections. While a work of this nature is challenging, no particular mathematical knowledge is assumed, the early chapters providing the essential background for the physical theories described in the remainder of the book. There is also enough descriptive material to carry the less mathematically inclined reader through, as well as some 450-500 figures. The book counters the common complaint that cutting-edge science is fundamentally inaccessible.