The organizational field (DiMaggio & Powell 1983) is one of the most inspiring concepts within the neo-institutional theoretical framework. Nevertheless, it is hard to operationalize fields where large and diffuse organizations exist. Where does an organization truly end? At its legal boundaries, at its various collaborative partnerships, or maybe even at the partners identifying themselves with an organization?

We would argue that the ego network of multiplex relationships determines the boundaries of a focal organization. The here presented approach shows how to dissolve nodes into smaller subunits and to allow for the modelling of fluid organizational boundaries by operationalizing boundaries as multiplex relationships. The approach is promising because large decoupled organizations such as universities are likely to span multiple boundaries. Only by adopting several types of relationships and dissolving nodes can the fluidity of large organizations be accounted for. The paper presents cases of organizations with strong and weak boundaries using data from the german field of research at the NIW www.niw.ie.edu .