This document summarizes a study examining the relationship between trade openness and city sizes using the New Economic Geography framework. The study finds that as trade openness increases, the size of main cities declines while the size of secondary cities increases. Similar results are seen for cities with over 1 million people. However, cities that make up a large share of the urban population do not see the same relationship with trade openness. The implications are that investment in infrastructure should target secondary cities during trade liberalization, especially port cities.