To date, over 2500 bilateral investment treaties (BITs) have been signed. The popularity of these treaties raises the question, what has driven the proliferation of BITs? Previous research argues that the proliferation of BITs is the product of competition for capital among developing states. This study hypothesises that the developed state transnational corporations (TNCs) are driving the spread of BITs. The results from a time series logistic regression support the TNC hypothesis, adding support to the argument that transnationals should be recognised as major actors in the international political economy.