On the basis of an exploratory case study, this paper is intended to provide understanding on the intricacies associated with the integration of firms with a business sector information infrastructure (BSII) such as a port community system (PCS). Although there is some research on the implementation of PCS, these studies have rarely addressed the issue of integration of preexisting systems. We address this gap with a case study of a PCS in a Spanish port community, which, moreover, complements prior studies by adopting a processual socio-technical perspective on integration. Finally we elaborate implications relevant to the implementation of BSIIs.