(Winner of the 2017 Paragraph annual essay prize competition, on the theme of ‘Belongings’) This article examines the ontology and politics of Peter Sloterdijk's Spheres trilogy, focusing in particular upon the notion of microspherical enclosure explicated in the first volume of this series. Noting Sloterdijk's unusual alignment of his philosophy with media theory, three main contentions are put forward. Firstly, that Sloterdijk's reconfiguration of Heidegger's fundamental ontology represents a largely unacknowledged renunciation of the primacy of Being-towards-death in the authentic existence of Dasein, foregrounding instead an originary co-belonging between mother and child. Secondly, that Sloterdijk borrows from media theory a concern...