This thesis examines organizational use of social media. It focuses on developing an understanding of the ways by which social media are used within formal organizational settings. From the vantage point of this thesis such an understanding can be achieved by looking at tensions and incompatibilities that might potentially exist between social media and organization because of their distinct characteristics. It is argued that the distinct characteristics of social media (e.g. openness, transparency, flexibility, etc.) and organization (e.g., hierarchy, formal relationships, standard procedures, etc.) may engender tensions and incompatibilities that affect the ways of using social media and their potential in organizations. The main premise here is that the possibilities, behaviors and practices afforded by social media are recognizably different in nature from common and established organizational practices, behaviors, norms and routines. Through a structurational understanding of organizational use of social media, influenced by Giddens’ theory of structuration and Orlikowski’s practice lens for studying technology use, this thesis offers the perspective of immiscibility to capture tensions and incompatibilities driven by the distinctive characteristics of social media and organization. It basically offers a way of seeing social media use in organizations as a dynamic, in-practice interplay between social media and organization characteristics. One key argument in this thesis is that the immiscible interplay of social media and organization, produces, at least in transition, ‘a bureaucracy of social media’. Social media, it is argued, are used in ways that are essentially bureaucratic, reflecting and also reinforcing established characteristics of formal organizations through the production and reproduction of structures which are driven by the immiscible interplay. The development of such an understanding was achieved through multiple research studies focusing on the use of the wiki technology for knowledge collaboration and sharing practices in two large multinational organizations: CCC and IBM. A number of qualitative methods were used in these studies to collect empirical evidence from the two organizations including interviews, field visits, observations and document analysis. The overarching contribution of this thesis centers on offering a unique way of understanding organizational use of social media by putting forward tensions and incompatibilities between social media and organization and also by providing an understanding of how such tensions and incompatibilities affect the potential for change by social media.