This book explores the lore behind iconic monsters in an in-depth and interesting way, shedding light on and bringing to life to iconic favorites such as beholders, giants, hags, and gnolls.
It also features several new monsters and dozens upon dozens of old monsters updated for 5th Edition. On top of that the book introduces new playable races including goblins!
If you want to add more options to your game as DM or as a player, look no further than Volo's Guide