In the strategic alignment model of Henderson and Venkatraman (1993) [1] IT infrastructure has an important but only implicitly defined role. According to evolving literature, IT infrastructure serves many different purposes in large companies. We outline the main missions (roles) of the corporate-wide IT infrastructure and its contribution to IS effectiveness and study the relationship of IT infrastructure with alignment processes and strategic integration. Our empirical tests with data from almost one hundred large companies resulted in three IT infrastructure roles, which reflect the IS communality, strategic, and flexibility dimensions of the corporate-wide IT infrastructure. The roles were not symmetrically related to the IS effectiveness and alignment perspectives. IT infrastructure roles had a significant interplay with strategic integration in improving IS effectiveness. However, the interplay of IT infrastructure roles with alignment perspectives had only marginal effects. Implications of the results for research and practice are discussed.