Since its increase in popularity in the 1990’s, mainstream knowledge management research has grappled with problems of capturing, storing and disseminating knowledge in order to support growth and learning in organisations. Attempts by management to impose knowledge management initiatives often ignore the fact that, as knowledge workers, many employees possess a huge array of work-related tacit knowledge, which cannot readily be made explicit through formal enterprise knowledge management systems and processes. Informal collaborative software, known as Wikis, may provide a more appropriate knowledge management capability and environment to capture tacit knowledge. However Wikis are only now moving from the social to the corporate arena because they challenge management authority by engaging the knowledge worker in democratising organisational knowledge. Theoretical development is needed, accompanied by sound methodologies, to better understand these new processes of creation, accumulation and maintenance of knowledge in organisations. This paper has addressed the gap between theory and method by using Activity Theory to analyse the Wiki as a tool that mediates employee-based knowledge management activities.