This chapter explores the dynamics of knowledge and authority within virtual communities, where participants contribute asynchronously to shape collective understanding around specific topics. Through the interactive sharing, modification, and recirculation of information, participants recognize cognitive authority in online interactions. The notion of authority is examined across various domains: in business, authority transcends expertise to include digital presence and persuasive influence, quantified by metrics such as follower counts. Similarly, in health communities like PatientsLikeMe, personal experiences often hold sway comparable to conventional medical advice, particularly in less-researched medical conditions. Such experiences contribute significantly to medical knowledge and research, bridging gaps left by formal studies. The chapter highlights qualitative aspects of authority, emphasizing active engagement and adept use of linguistic resources to establish credibility and influence. It underscores the negotiation of authority among participants, where legitimacy enhances the capacity to claim authority within hierarchical online structures. By analyzing interactions and recognition within these communities, the chapter elucidates how individuals emerge as authoritative voices, shaping the production and legitimization of knowledge in different fields.