 A history of ideas about consciousness and intentionality could easily take us further into the past than this article can cover. A convenient, relatively recent starting point would be in the philosophy of Franz Brentano. He more than any other single thinker is responsible for keeping the term “intentional” alive in philosophical discussions of the last century and a half or so, with something like its current use, and was much concerned with its relationship to consciousness (Brentano [1874] 1973). Brentano himself was quite aware of the deep historical background to his notion of intentionality: he looked back through scholastic discussions (crucial to the development of Descartes’ immensely influential theory of ideas), and ultimately to Aristotle for his theme of intentionality (Brentano [1867] 1977). One may well go further back, to Plato’s discussion (in the Sophist, and the Theaetetus) of difficulties in making sense of false belief, and yet further still, to the dawn of Western Philosophy, and Parmenides’ attempt to draw enormous consequences from allegedly finding that it is not possible to think or speak of what is not. In this section, we will review how Brentano conceived of intentionality and consciousness, and their relationship, and how that conception was transformed in the thought of his student Husserl—whose name is that most strongly associated with the phenomenological movement—and in the writings of some of those he strongly influenced. This will allow us to introduce the three themes mentioned in the introduction—detachability, basic forms, and reflexivity—by which one might unify the disparate discussions of consciousness and intentionality arising over roughly the last century.