On the theoretical side, coordination is a critical issue for MAS engineering, since it deals with modelling and managing the ever growing complexity of the agent interplay within a MAS. On the practical side, the availability of powerful and robust infrastructures is a key factor to enable and promote MAS as a mainstream software engineering technology. By adopting Activity Theory as a unifying framework for the many existing approaches to MAS coordination, we put forward the notion of artifact as a key concept for infrastructures, from which we derive some distinctive properties that a coordination infrastructure should feature. Finally, we discuss how a principled approach to MAS engineering based on coordination infrastructures could be built around such a notion.