The innovative progress in Information Technology and the formidable competitions have been making many companies to introduce ERP systems, CRM systems, SCM systems and so on. These information systems are being adopted in the form of the packaged software rather than the custom development. A common problem when adopting packaged software has been the issue of gaps between the functionality offered by the package and that required by the adopting organization. As a result, organizations have had to resolve these gaps to take the full advantages of packaged software. ERP systems have the characteristics of packaged software. This research investigated the gap resolution strategies and the factors that are considered when choosing a resolution strategy. To reveal how the gap resolution strategy is chosen, a multiplecase study was conducted on the 4 big companies in South Korea. This study revealed five gap resolution strategies were used to resolve the gap between ERP systems’ function and the organization requirements-The use of legacy system, addon development, new development, BPR, modification. The level of the gap, the size of the gap, the importance of the function with gap, the extent of the integration with other modules or functions, the knowledge on the ERP systems development language, and the cost of implementation were considered when choosing the gap resolution strategy. These factors were taken into consideration in sequence rather than in a simultaneous order, forming the decision tree for the gap resolution strategy choice.