The Greater and Lesser Keys of Solomane are a pair of demonological grimoires of unknown authorship. The Greater Key is a treatise in two sub-sections; the first describes the general principles of ritual sigils, magic objects, and theories of the magical nature of various classes of beings from several different realms, while the second explains and provides frameworks for summoning, constraining, cursing, coercion, and dismissing and banishing spells. The Lesser Key is a compilation of the True Names and corresponding ritual magical sigils of a number of specific creatures who are thought to be sometimes amenable to making deals, or, to a sufficiently wiley sorcerer, of being coerced to serve. Because the two books are complementary to each other, they are usually both found together in a single volume.
These grimoires have always been very rare and considered very dangerous. Most (though not all) mages and wizards who discovered copies realized the hazard they represented and had them destroyed via the appropriate magical means.