The Ultimate Discworld Companion

The absolute, comprehensive, from Tiffany Aching to Jack Zweiblumen guide to all things Discworld, fully illustrated by Paul Kidby.
The Discworld, as everyone knows, is a flat world balanced on the back of four elephants which, in turn, stand on the shell of the giant star turtle, the Great A'Tuin, as it slowly swims through space.
It is also the global publishing phenomenon with sales of over 70 million books worldwide (but who's counting?). There's an awful lot of Discworld to keep track of.