International trade theory offers hypotheses about how globalization affects income inequality both between countries and within countries. Since technology flows from rich to poor countries, differences between rich and poor are greater than differences among rich countries, and poor countries are likely to gain more from the trade gains due to lower living costs, globalization is likely to improve global inequality.  Inequality within nations has been studied by the Stolper-Samuelson theorem and it is here argued that the theorem gives an oversimplified picture.