From the preface:
"The TOME OF MIGHTY MAGIC was written and published as a supplement to the growing field of fantasy roleplaying games. Within this book an attempt is made to bring forth a new series of ideas, i.e. spells. Contained within this book are some spells that the great spell casters Aluap, Eridor, Ida and Nimanril used in their campaigns many eons ago. Now they pass them on to you."
A book of spells, designed for 1st edition Advanced Dungeons and Dragons (though not explicitly stated as such). Levels of spells are from 1st to 20th level, for all magic-using classes.