This project aims to transform our understanding of mental and linguistic representation, its nature and significance for explanatory projects inside and outside philosophy. It seeks to show that the contemporary trend towards “deflationary” and non-explanatory treatments of representation is misguided, and that a naturalistic treatment of representation is available. By bringing together contemporary work in metaphysics with the lessons of the naturalizing projects of the 80s, I can make a breakthrough in the philosophical account of the mind in nature.I will shows that the key to the correct understanding of the representational relation is to develop the correct conception of the media of representation---the metaphysics of words, in the case of language; and the metaphysics of thought, in the case of mental representation. This topic is neglected, or studied only in abstraction from the metaphysics of representation. But I show that the true value of the groundbreaking approaches developed in the 80s lay in providing a satisfactory individuation of syntax---which provides a basis for resolving outstanding puzzles for interpretationist theories of semantics. This allows a synthesis of the two leading traditions in the foundations of representation. I develop the unified theory in unprecedented detail, use it to pinpoint what goes wrong in recent trends in the field, and examine its interactions with cutting edge problems in philosophy.The project will open up new approaches to the philosophy of representation, shed new light on the relation between language and thought, and develop a systematic and unified account of the nature, explanatory role, and epistemology of representation.