Given his proximity to the Marburg School that was central to the inauguration of Cusa Scholarship in the twentieth century, it is surprising how inessential Nicholas of Cusa remained for Martin Heidegger. This absence is especially marked in Heidegger's Destruktion of the onto-theological character of metaphysics, where Cusa is at a remove from any of Heidegger's inflection points in the history or destiny [Geschick] of Being. This situation could not be more different for Jean-Luc Marion, who adopted Heidegger's project of dismantling the onto-theological character of metaphysics, even if he assigns differing conceptual and historical coordinates to his understanding. For Marion, onto-theology results in a sort of 'conceptual idolatry' where God is submitted to a predetermined concept of being of our own making. Within his own framework of onto-theology, Marion's understanding and use of Nicholas of Cusa could not be more essential, signalling a path beyond any metaphysica generalis that is the subject of Heidegger's critique. This paper deals with the reception of Nicholas of Cusa in Heidegger and Marion's understanding of onto-theology. My argument is that the difference between their readings and reception of Cusa is rooted in their respective understanding of the Neoplatonic 'beyond-being.' As Werner Beierwaltes has shown, Heidegger is almost systematically unable to engage with Neoplatonism without taking the One for a summum ens. For Marion, on the other hand, his understanding of onto-theology as resulting in a conceptual idolatry entails that any correct way to deal with onto-theology is precisely by providing a route beyond the concept of being. In spite of their apparently shared critique, their respective uses (or non-uses) of Cusa show the most striking difference in their understandings of being in general and then of onto-theology in particular.