The rate of failure for international mergers and acquisitions (M&As) is exceptionally high, since the integration of merging firms does not function well. Using a process perspective, this study aims to analyze the integration process in a cross-border merger and the development of a common organizational culture. A framework based on premerger cultural and organizational fit, synergy, and resulting organizational culture is developed to study the growth of Nordea, a merger of four Nordic banks. Data include in-depth interviews and secondary sources. This case study shows how cultural and managerial differences are dealt with and synergies realized. Building a broad organizational culture involving human resource management, decision making, technology, competitiveness, and customer relationships is necessary for merger integration, but it is costly and difficult. We suggest that success in mergers lies in managers creating a new cultural identity with unique values and perspectives.