Social media technologies are increasingly used within organizational settings. Particularly, organizations continue to adopt and use wikis for enabling collaboration among their professional communities of practice. At this respect, the current paper reports results from an interpretive case study focusing on the use of a wiki for knowledge collaboration and sharing at a large multinational organization. It examines how the wiki is used by members of several professional communities of practice through interviews, observations, field studies, and documents. It concludes by showing that the openness of the wiki has a dual impact on wiki collaboration and also discusses how the wiki might serve as both an enabler and inhibitor for community and knowledge collaboration.