The advent of the future Internet-of-Things brings about increasing complexity and diversification of Enterprise Information Systems, which makes interoperability a critical requirement towards their scalability and sustainable development. This is especially evident in the disaster management area, which typically involves a highly heterogeneous set of institutions and organisations responsible for delivering emergency response services who often fail to rise up to the task, mainly due to a lack of proper collaboration. As the legacy consideration of the interoperability paradigm appears to fail in meeting these challenges, in this paper we define Interoperability as a Property (IaaP) of every ubiquitous system. In doing so, we use an anthropomorphic perspective to formally define IaaP’s enabling attributes (namely, awareness, perceptivity, intelligence and extroversion), with the objective of taking initial steps towards a Theory of Interoperability of Everything (IoE). The identified concepts and their interrelations are illustrated by the presented IoE ontology.