Transactive knowledge, i.e. knowing who knows what within a team setting, has been identified as a key factor for explaining the combination of individual knowledge, skills, and abilities (KSA) in the socio-cognitive team research. To know what others know helps team members in better searching and retrieving relevant information. Transactive knowledge therefore may lead us to open the black box of the evolution of team-based competencies, too. It can be divided into task-related and biographical knowledge about our colleagues. It also includes a precise understanding of team members’ personalities and their status as well as the knowledge about their social ties outside the team. Finegrained knowledge about each other affects the efficiency and smoothness of cooperation among team members. We provide an explanation on how it actually can be managed, after showing the basic functions of transactive knowledge. Besides the technological infrastructure fostering communication processes, the analysis of the team task offers information on the requirements for the development of transactive knowledge: The task complexity decides about whether transactive knowledge is a means to substitute for one another (as it is the case for simple tasks on the shop floor), or whether it is used as a means to create a transspecialist understanding (as it is the case for highly-qualified workers, e.g. in new product development teams). Task interdependence on the contrary decides about how important the development of transactive knowledge generally is. Without intensive interaction the training of team members to build up transactive knowledge will be nothing but a waste of resources. We therefore focus on highly interdependent project teams consisting of members being not familiar with each other, i.e. members who work together for the first time. Two training sequences are discussed in detail: Knowledge disclosure and knowledge updating. In the first training sequence knowledge about one another needs to be disclosed, preparing the team to perform well. Cross-training is an appropriate training instrument in this context. Cross-training refers to a strategy in which each team member is trained on the tasks, duties, and responsibilities of his or her fellow team members. It consists of positional clarification, positional modeling, and positional rotation. The second sequence is used in teams while performing. For successful teams it is necessary to maintain team situation awareness, i.e. to create a shared understanding of what is going on. This is crucial for recognizing changes of members’ KSAs and changes in the environment. Without interpersonal feedback situation awareness can hardly be achieved. The after action review (AAR) which has its origin in the US Army is an instrument being able to effectively institutionalize such task-oriented feedback processes. Four basic questions are to be answered in regularly team meetings: What happened? What should have happened? Why did it happen? What can we do better? The AAR is not only essential for creating situation awareness but also for updating knowledge about one another. Finally, open questions are discussed.