One of the great challenges of interdisciplinary education is to create sufficient cohesion between disciplines. It is suggested that cohesion depends on the transfer of knowledge (in a broad sense, which includes skill and competences) among the disciplines involved. Some of the most characteristic types of such transfer are identified and analyzed: Transfer of factual knowledge, theories, methods, models, skills, modes of collaboration and organization, meta-competences, disciplinary self-consciousness, problem selection, framework construction and motivation. Though some of these types of transfer may have a greater or smaller potential for creating cohesion, different kinds of cohesion may serve different interests, and there is no reason to assume that e.g. joint problem solving or theoretical integration should be more conducive to cohesion than e.g. contributions to motivation or disciplinary self-consciousness.