Six Sigma is one of the most successful improvement strategies of the last 5 decades and has been implemented worldwide by organizations in different sectors and sizes. Despite the popularity, 60% of all Six Sigma initiatives are abandoned or end in failure. Therefore, the purpose of this thesis is to investigate what factors large manufacturing enterprises in Sweden need to prioritize to introduce Six Sigma successfully. The research was conducted as a holistic multiple-case study where qualitative data was collected through semi-structured interviews with three companies. A thematic analysis was made to identify patterns between the companies about critical success factors associated with Six Sigma, Change Management, and Organizational culture. It was shown that Company 1 has introduced Six Sigma but has no defined plan on how to move forward with the initiative. Company 2 has fully introduced the method and is actively working with it, while Company 3 has failed with the introduction of Six Sigma. All identified factors were rated as either a success or a failure factor for each case company. The success factors differentiating Company 2 from the other case companies have been evaluated to be the most critical success factors. Top management commitment, Organizational support, Organizational culture, Communication, and Strategic plan have been identified as the most critical success factors that must be prioritized to introduce Six Sigma successfully. Furthermore, cultural factors such as communication between departments, supportive managers, and committed top management have been identified as important to introduce Six Sigma successfully. The results of this study can be applied to successfully introduce change initiatives in large manufacturing enterprises in Sweden.