We discuss a unified theory of directed technological change and technologyadoption that can shed light on the causes of persistent productivity differencesacross countries. In our model, new technologies are designed in advanced countries and diffuse endogenously to less developed countries. Our framework is richenough to highlight three broad reasons for productivity differences: inappropriatetechnologies, policy-induced barriers to technology adoption, and within-countrymisallocations across sectors due to policy distortions. We also discuss the effectsof two aspects of globalization, trade in goods and migration, on the wealth ofnations through their impact on the direction of technical progress. By doing so,we illustrate some of the equalizing and unequalizing forces of globalization.