Abstract. We propose a theoretical framework for the optimal collaboration among researchers in a knowledge network in which researchers are not limited to a single discipline and in which multiple modes of communication, including communication via the Internet, are available. We introduce a novel concept of distance to measure not only the communication distance but also the distance between disciplines. We formulate the knowledge network collaboration model as a variational inequality problem whose solution yields the optimal allocation of effort/time of the researchers as well as the associated opportunity costs. Key words: Knowledge networks, Scientific collaboration