Volo's Guide to Monsters

Volo's Guide to Monsters is a sourcebook that explores the lore, ecology, and culture of dozens of iconic D&D monsters, from beholders and mind flayers to giants and yuan-ti. It also introduces monstrous player character options like goblins, hobgoblins, kobolds, and tabaxi, plus a bestiary of new creatures. Written from the in-world perspective of the gnome sage Volothamp Geddarm (with corrections from Elminster), it is a treasure trove for DMs who want depth and adventure hooks.