In the last years the penetration of ERP systems within small, medium and large organizations increased steadily and led to a broad consensus within the business community about the benefits for organizations in different business sectors. To react to rapidly changing business environments, technological enhancements and rising pressure of competition, organizations are forced to adapt their ERP system and perform ERP upgrades. This thesis identifies 14 critical success factors for ERP upgrade projects based on qualitative interviews with CEOs, CIOs, ERP consultants and project managers who recently carried out ERP upgrade projects in their respective organizations. Among others, effective project management, external support, system testing, the composition of the ERP team and the usage of a multiple system landscape play a key role for the success of the ERP upgrade. Furthermore, a comparison between the identified critical success factors and critical success factors in ERP implementation projects discussed in literature was conducted. Even though there are many similarities between ERP upgrade and ERP implementation projects, some differences emerged, which have to be considered in detail to successfully carry out an ERP upgrade project.