Despite the fact that society and organizations rely heavily on Information Systems (IS) and software, the maintenance of vendor-supplied IS, in particular standard package software has gained little attention within the academic literature. This paper presents a conceptual study of the current state of research concerning the reasons for deferral and performance of vendor-supplied maintenance by the purchasing organization. These reasons have so far neither been investigated together nor from that perspective. Based on a systematic literature review and taking the purchaser's viewpoint, reasons for maintenance deferral and performance are identified from the literature. They build the groundwork and foundation for a Maintenance Lifecycle and Process Model that provides a starting point to research vendor-supplied maintenance from the customer's point of view.