The 13th Age Core Rules are required to use this book.

For Game Masters, 13th Age Glorantha includes:
More than 80 pages of monsters and enemies fully compatible with any 13th Age campaign, including Chaos priests, dragonsnails, scorpionmen, Crater Makers who call down the Moon, and the awesome Chaos demon known as the Crimson Bat.
More than 60 pages of ready-to-run adventures and heroquests-venture into myth to refight the battles of the gods and gain their cosmic powers!
A distinctive setting that will entertain longtime fans but is aimed at gamers who've never heard of Glorantha.

If you're a 13th Age player you'll find:
5 new classes, including the hell mother who summons Darkness spirits and giant spiders; the swordmaster Humakti who wields Death; and the trickster who funnels your bad luck onto your enemies.
5 new class variants, including the wind lord, a fighter with magical storm-related exploits; and the rebel, a rogue with the supernatural ability to get where he's not supposed to be.
2 new PC races, the trolls and ducks, plus Gloranthan humans with new cultural traits.