The proliferation of applications to support cross-enterprise processes has left companies nursing a collection of systems. The integration of such systems, within and across the organizational boundaries, remains a top issue of researchers and practitioners’ agendas. Although integration has long been treated as a key variable in the IS field, the construct has received little conceptual scrutiny. In this essay we argue that the concept of IOIS integration (cross-enterprise integration of information systems) is still ambiguous and lacks an understanding on its nature. Thus we explore prior literature that has attempted to conceptualize IOIS integration. We examine dimensions that concern both the methodology used (epistemology, theoretical perspective, research approach, duration of the study, conceptual model and unit of analysis), and the construct (scope, layer of integration and conceptualization of the ICT artefact). Sixty-one articles are reviewed. We present the results and discuss different dimensions of the construct (definition, antecedents, consequences and measures). The purpose of this literature survey is to shed some light on the IOIS integration construct as well as to uncover areas for future research.