A purported feature of Enterprise Systems (ES) is that they are “integrated”; meaning that they in some sense bring parts into a unified whole. However, it is far from clear what is integrated into what, or how integration is achieved in practice. Moreover, the very concepts of integration and other related, fundamental concepts such as ‘organization’, ‘coordination’ and ‘knowledge’ are abstruse. To this end, the purpose of this contribution is to make an inquiry into integration by departing from the perspective of integrationism; a new development in the theory of communication.  This view is further elaborated using Vygotsky’s distinction between lower and higher mental functions, and the notion of activity modalities suggested by Taxén.  Integration thus conceived provides a foundation from which inquiries into ESs, both from a theoretical and practical point of view can be carried out. The ideas in the foundation are illustrated by some examples from the Ericsson telecommunication company. A sketch of an ES implementation method is outlined. The main conclusion is that a thorough ground for advancing the knowledge about Enterprise Systems can be established only if our unique human predispositions for coordinating and integrating actions are considered; something which may have far-reaching consequences for advancing our knowledge about Enterprise Systems