From the publisher's Website:
Iconic monsters for your D&D campaign.
This core rulebook packs in over 200 new monsters to menace D&D player characters. Classic monsters such as the derro, the mimic, and Lolth (Demon Queen of Spiders) make their first appearance here. In addition, this book includes scores of new monsters to challenge characters of heroic, paragon, and epic level, including deadly catastrophic dragons!