It is well known that the quantum theories introduced radical changes in the conception of matter. However, there is no consensus on which these changes are, or on what their impact on philosophy is or should be. Whereas some scholars have stressed the changes in physical theory, others have claimed that the quantum theory has forced us to give up the realist postulate that there are things in themselves, that is, things existing independently of the knowing subject. Having dealt elsewhere with the latter (or Copenhagen) interpretation (Bunge 1959b, 1967b, 1973a, 1985), I will concentrate here on the new ontology necessitated by the quantum theories.