Shared service centers (SSCs) are an increasingly important and oft-utilized approach to organizing Information Technology services. Nevertheless, researchers hitherto have not investigated SSCs sufficiently. Our research attempts to fill this gap by addressing the following basic problems: Firstly, no standardized definition of SSCs has established; and, secondly, different features of SSCs in practice have not been analysed. In an extensive literature review, we identified the following characteristics of SSCs to be commonly mentioned by researchers: consolidation of processes within the group; delivery of support processes; separated organizational unit; alignment with external customers; cost cutting as a major driver; focus on internal customers; and operation like a business. In a focus group, we identified the following parameters in which existing SSCs differ from each other: legal form; main form of co-ordination; service charges; external market; contractual form; center concept and product portfolio. These criteria were validated empirically by extensive case study research with seven IT-organizations from North America and Europe.