The dissertation consists of a reflection on the notion of existence. At first, a brief exposition about St. Anselms ontological argument and the kind of conception of existence that it demands is made. After that, a brief investigation regarding the vision of the notion of existence of three main pillars of our philosophical tradition - Hume, Kant and Frege - is undertaken. To a certain extent, their conceptions are studied separately, so that the main aspects and peculiar outline that they convey to the notion of which they intend to give an account can be brought to light. Subsequently, these conceptions are put side by side in a comparison of some of their most relevant similarities and discrepancies. This study is followed by a critical investigation. First, its negative part is exposed: some observations regarding problems involved in each one of the kinds of conception of existence exemplified in the precedent parts, mixed with reflections on the relation between existence and notions such as that of individual and quantification to which they give rise. Secondly, its positive part: based on the observations already made, some suggestions on how to give an account of some relevant aspects of the notion of existence. The dissertation also contains an appendix in which a brief incursion in the aristotelian thought is undertaken. More specifically, it consists of an investigation regarding the relation between existence and quantification in the context of the theory of the square of oppositions as formulated in the famous treatise De Interpretatione.