Tacit organizational knowledge is intangible, implicit, and profoundly attached to people (Spender, 2003). While highly complex, it is also a driving force of organizational performance, and its transfer crucial in capitalizing on existing resources (Cross & Baird, 2000). Spender (1998) suggested that tacit knowledge may represent an alternative system of organizational knowledge, and this author investigated this notion. This research is built upon empirical evidence from six knowledge transfer case studies so as to examine tacit knowledge and provide insight into what makes it tacit. Nine distinct, however not mutually exclusive types of tacit knowledge were identified through this research: Skill, Cause-effect, Cognitive, Composite, Cultural, Unlearning, Taboo, Human, and Emotional. Each type can be discerned with its unique set of elements that is essentially responsible for it being tacit, or subjective. In addition, the relationship between the problematic nature of knowledge and its transferability is explored. Various knowledge transfer channels are examined for their richness. Results indicated that no transfer channel was rich independently of the knowledge it transfers, and that all effective channels involved an active ‘pull’ of the knowledge by its recipient.