I now have everything I need should I actually want to run a game of Pathfinder. Along with the Core Rulebook and the Rise of the Runelords Adventure Path, the Bestiary makes up what I consider the ‘base set’.
‘Bestiary’ means a Compendium of Beasts, like in the middle ages. It is the Pathfinder version of the D&D Monster Manual.
It is a lovely hardback encyclopaedia with over 350 monsters, each with its own colour illustration. It has all the old classics from my 1978 AD&D Monster Manual, but with lots of extra background info, and appendices with ideas on how to use them all.