Today's organizations are characterized by digitization, development and growth. A wellimplemented ERP-system that match the processes of an organization can lead to a number of benefits. ERP-implementations and critical success factors are a well-researched area. Nevertheless, a great number of ERP-implementations are still considered as failures, which makes further research around the area considered relevant. This study aims to investigate what is critically related to important success factors in implementing ERP-systems. The study began with a literature study in which 15 scientific articles were reviewed, of which 69 success factors were identified. Of those, the six most common were selected as the basis for this study. In order to answer the purpose of this study, interviews were conducted with project managers who had a lot of experience from ERP-implementations. Using the results from these, as well as the collected theory, comparisons have been made between them. This, in turn, has resulted in a finding that communication is a key part of the entire ERP implementation and in all the critical success factors investigated in this study. Hence, the interaction between supplier and customer is seen as critical in ERP implementations, so they understand each other, have shared expectations and a realistic commitment to ERP implementation.