This chapter aims to determine how think tank networks came into being by putting forth a series of theoretical hypotheses to address this issue. First, it can be expected that what has a remarkable effect on the size of think tank networks is the time and energy think tank leaders spend on social activities. For this reason, inputs into social activities serve as the control variables to explain the size of think tank networks. This chapter discusses additional factors (beyond time and energy input) involved in the special profession as think tank leaders to determine the size of networks, focusing on three related theses.