This article re-conceptualises the ‘constitutive outside’ through Roberto Esposito’s theory of immunity to detach it from Laclau and Mouffe’s political antagonism. It identifies Esposito’s thought as an innovative epistemological perspective to dissolve post-ontological political theories of community from the intertwinement with a foundational self/other dialectic. Esposito shows how a community can sustain its relations through introversive immunisation against a primarily undefined outside. But it is argued that his theory of immunity slips back to a vitalist depth ontology which ultimately de-politicises (...) the construction of the communal outside. This article draws on Niklas Luhmann’s immunity theory to resituate immunisation in the political production of social connectivity. Following Luhmann, politics relies on immunisation through contradictions to reproduce its functional role as a decision-making institution, but is at the same time constantly exposed to potential rupture through the political openness immunity introduces. Through Esposito and Luhmann, this article identifies the relationship between a social inside and its outside as open-ended and secondary to an introversive process of socio-political self-differentiation. It can involve, but does epistemologically necessitate, the construction of an external other. (shrink)