Expedition to Undermountain is a combination sourcebook/campaign adventure for adventurer levels 1-10. This is the D&D 3rd edition supplement for Undermountain. The book is split into an Introduction, briefly describing Halaster's death and a synopsis of the adventure, the first chapter, which briefly describes Undermountain, with maps of most levels and sublevels, chapters 2-5, which are the campaign adventure, and an appendix of new creatures, such as the Eyeball Swarm, and new items, such as the Crown Adamant.