The Picatrix is long, roughly four hundred pages in modern editions, and it is a working manual rather than a treatise. Its four books set out how to make astral talismans: what image to engrave, in what material, at what astrological moment, with what suffumigation and what invocation, in order to draw down the power of a planet or a star for a stated purpose. Those purposes are entirely practical and often unedifying, running to love, wealth, the ruin of an enemy and the destruction of a city.
It is also a philosophical work, and the two halves sit awkwardly together. The theoretical passages present a Neoplatonic cosmology in which the operator works with the natural sympathies of a living universe; the operative passages describe rites involving blood, unpleasant ingredients and prayers to planetary spirits that are hard to read as anything but address to a god.
That combination made it the most compromising book a Renaissance scholar could own. It circulated widely in manuscript and was not printed, which is itself informative: the Latin version, made for Alfonso X of Castile in the thirteenth century, was too useful to destroy and too dangerous to publish.
Modern scholarship has largely detached the work from al-Majriti, the Andalusian mathematician whose name it carries, and treats the Arabic original as an eleventh century compilation drawing on much older Hellenistic and Harranian material.