Existing research on the determinants of international trade tends to examine the impact of aggregate joint IGO memberships, and has done little to separate IGOs into various function types. Using a new IGO dataset and a novel network analysis approach called the temporal exponential random graph model (TERGM), I assess the importance of three main IGO types -- economic, social and general purpose -- in helping states to establish major trading relations. The results provide support for the importance of general purpose IGOs in forging strong bilateral trade, and also draw attention to endogenous network structures such as popularity and triadic closure effects. A robustness test further reveals that PTAs and other economic IGOs such as regional banks are also instrumental in fostering major trading relations. This thesis presents a more nuanced way of analyzing IGOs and provides the impetus for the study of network effects in international trade.