This chapter provides a general overview of the relations between international trade and the economy of Southeast Asia from a long-term perspective. After the short description about the relationships between natural endowments and international trade of Southeast Asia before the European arrival, this chapter is devoted to an analysis of international trade of Southeast Asia since the sixteenth century by focusing on the economic influences of international trade on the Southeast Asian economy and society. Southeast Asia has been in touch with a wide range of overseas markets in Asia and Europe. Large demands for Southeast Asian products have stimulated the economic development of the region. The economy was largely developed for the mass production of primary products. Development of the delta areas, introduction of the plantation system, and the acceptance of Chinese immigrants are good examples of the region’s capacity to respond to changes, before the production of manufactured goods became more important in the late twentieth century.