From the back cover:
H.P. Lovecraft coined the term "Yog-Sothothery" to refer to the fictional myth cycle he invented for his tales of cosmic horror. These creations have been adapted and expanded by many subsequent writers and game designers, to fuel myriad stories and games. This book aims to pare back this complex tapestry of horrific shared world-building to present JUST the original creations of Lovecraft as he himself imagined them, with game statistics to allow their easy use in any "evolved D100" roleplaying system. Infuse your games of cosmic horror with terrors drawn from the original tales that kick-started the Cthulhu Mythos…
Included in this book are ready-to-play game adaptations of many of Lovecraft's most famous horror creations:
40+ entities (eldritch gods and unspeakable races)
30 Lovecraftian rituals and weird, alien artifacts
Mythos tomes including the infamous Necronomicon
a selection of cults and Mythos-aware organizations
a grab bag of unnatural sites tainted by the Mythos