Organizations decide to merge or take over other organizations in order to increase competitiveness in the market, create value for shareholders and improve efficiency. During mergers or take overs, in addition to integrating business systems, it is also necessary to integrate the cultures of two organizations into one. Knowing organizational culture, its elements, dimensions, functions, models, categories and types enables easier modification of organizational culture. Different types of mergers and acquisitions of organizations define the direction of the change of organizational culture. A change in the organizational culture is accomplished by a change in the employees' value system and behavior, so it is essential to ensure management and support of the employees during the takeover or merger of organizations. Communication, motivation, organizational justice, organizational loyalty of employees are key in the process of taking over and merging organizations. The role of management is to establish a team of people who would carry out the change process of the organizational culture, and who would clearly and timely communicate the necessary information to the employees. Three cases of takeover of organizations are described – one takeover of an organization abroad and two takeovers on the domestic, Croatian, market. The cases indicate the importance of presence of a management team that leads the change of organizational culture and the importance of communication during the merger or takeover of the organizations. A change in the organizational culture should result in a new organizational culture that will enable employees to successfully operate and work within their organization.