Horizontal mechanisms are structural overlays (such as roles and groups) and non-structural devices (such as physical colocation) that are designed to facilitate cross-unit collaboration. The objective of this study is to increase our cumulative knowledge about what top-down mechanisms are being used to promote the coordination of IS activities across corporate/division boundaries. Propositions about how mechanism usage differs under centralized versus federal IS organization contexts are developed based on a synthesis of prior organization science and empirical IS literature. Multiple methods are used to collect data from IS and non-IS senior managers from two case sites with theoretically different IS coordination needs. As predicted, multiple types of structural and non-structural mechanisms were implemented for business-IS coordination in the company with a centralized IS context, and for corporate IS-decentralized IS coordination in the company with a federal IS context. An unexpected finding was that mechanisms for both of these kinds of IS coordination were valued at each case site. The prediction that a formal group mechanism would be perceived as more effective for achieving cross-unit coordination than an integrator role mechanism was not supported. The article concludes with a discussion of implications for research and practice.