The investigation of sustainable enterprise interoperability requires an explicit position of what constitutes the enterprise. In particular, human aspects like agency, sense-making, interpretation, common understanding, etc., must be taken into account. To this end, the purpose of this contribution is to make an inquiry into interoperability from the perspective of the Activity Domain Theory (ADT). In this theory, the enterprise is considered as a constellation of activity domains. The activity domain is characterized by the activity modalities -objectivation, contextualization, spatialization, temporalization stabilization, transition -which represent human, innate predispositions for coordinating actions. Interoperability is focused to one particular modality: the transition between activity domains. An example from the telecom industry is used to illustrate the approach. Implications for various aspects of interoperability are discussed. In conclusion, it is argued that the ADT is an alternative framework for advancing the understanding of sustainable interoperability between enterprises and enterprise systems.