There is ample evidence of deviations between the actual and planned interaction structures between a firm's IT department and business units. Such deviations can hinder senior managers from governing their IT organizations effectively because they do not know how
work really gets done. This paper develops an explanation for why actual structures differ from planned structures. Understanding this phenomenon is indispensable for managers to govern the real organization, to uphold compliance with important standards (e.g., ITIL, COBIT), to decide whether the formal or the actual organization is more effective, and, finally, to identify management actions that support the optimal structure. To develop this understanding, we analyze the interaction structures at the interface between firms' business units and IT units in four rich cases, using data from 56 interviews and 47 questionnaires, and applying qualitative methods and social network analysis, which give us deep insights into planned and actual interaction among employees. We test two different
explanations for deviations of actual from planned interaction structures and find that boundary-spanning theory provides the dominant explanation for such deviations: Inclined to span the business/IT boundary most effectively, the actors involved deviate from planned
structures especially when other structures offer better boundary-spanning potential, which is influenced primarily by cross-domain knowledge. In addition, relationships also play an important role. On the positive side, relationships provide opportunities for such deviations, while on the negative side, a conflict-laden relationship might hinder deviations even if they were advantageous.