First Published in 1997. The explosive growth of world trade in the last three decades is unparalleled in history, both due to the rapid increase in volume and to the change in the composition of trade. Historically, trade between nations has consisted largely of exchanges of products that were very different from each other, neither closely substitutable in consumption nor production processes. However, in this latest period of trade expansion, the majority of the increase in world trade has been in manufactured goods, many of which are highly substitutable differentiated products. This has led to growth in intra-industry trade, the cross-shipment of similar products. This study links increased shares of intra-industry trade with growth in newly-industrializing countries. To examine these questions, this study first gives a review of existing literature, both theoretical and empirical. Five hypotheses on intra-industry trade are then discussed. A model is then presented and estimated, using data on bilateral trade between the United States and its five major trading partners, Canada, Japan, France, Germany, and the United Kingdom.