Margaret Cavendish was the first woman to develop her philosophy through a series of treatises. Her innovative rethinking of received notions of substance, accident, matter, body, and soul allowed her to elaborate, in several major works published between 1653 and 1668, a novel account of the material world. She developed original accounts of theoretical notions like causation and divisibility, and boldly idiosyncratic accounts of properties like color and heat. I propose to investigate, contextualize, and explain several signal features of her metaphysics. A recent renaissance in Cavendish studies has made it possible, for the first time, to begin to fully appreciate her insights, and in this project I will give a full-dress account of her metaphysical theorizing that reveals not only its deep relationship with and advantages over Cartesianism, but also the sometimes puzzling appropriations and reinterpretations of Scholastic thought that resulted in a centuries-long failure to appreciate Cavendish's philosophy, which is only now being remedied. In a series of papers and a book project, I propose to show how, in Cavendishian trialism, animate matter, inanimate matter, and their contingently blended unity, the material world as a whole, together provide a solution to the mind-body problem that does not founder where Cartesian dualism does, but that actually has the resources to make the Cavendishian analogue of what is known to scholars as Cartesian trialism work.