The volatility in emerging market finance over the last decade has highlighted the importance of developing equity exchanges to enhance risk sharing between international investors. Debt markets do not allow for as much risk sharing. Theoretically, stock market development involves trading externalities, as the decision by one firm to list provides a positive spillover for other firms considering an initial offering. This theory thus has a clear policy implication in terms of deliberate government action to promote stock market development. This paper tests empirically for the existence of trading externalities in developing countries, and finds evidence of such externalities for Latin American, but not Asian, stock markets.