S. Petersen's Field Guide to Cthulhu Monsters is a 64-page sourcebook that details 27 creatures of the Cthulhu mythos, each with a full-page full-color painting and clues to help characters recognize them, and the supplement includes a key to help identify the monsters and a chart displaying their relative sizes.

[1] S. Petersen's Field Guide to Cthulhu Monsters was written by Sandy Petersen with Lynn Willis, with art by Tom Sullivan and was published by Chaosium in 1988 as a 64-page book.

[1] In the October 1988 edition of Dragon (Issue #138), Ken Rolston called this "a useful game reference" that "manages to take itself fairly seriously while maintaining an atmosphere of fun."

Rolston called Petersen's writing "a perfect example of Chaosium’s masterful control of tone and diction."

Buy several for your best friends and hope that some day the gaming hobby will produce works of equal charm to describe monstrous species for other fantasy and science-fiction role-playing settings.