We deliver the translation of Book Z of Aristotle's "Metaphysics", which is based on the authoritative edition of the Aristotelian text by the Englishman W. D. Ross. We consider Book Z of the "Metaphysics" by the philosopher from Stagira to be particularly important, as in this book the philosopher arrives at the radical definition of substance as the combination of form and matter, thus formulating that each individual or thing constitutes a distinct substance. In this way, the Platonic philosophy is surpassed, which considered that substance as an idea exists outside individuals and things, in the world of ideas. Aristotle inaugurates the purely anthropocentric era of philosophy by placing substance within human existence through this book of the "Metaphysics".