This document discusses various theories and concepts related to international trade. It begins by explaining why nations trade, which is generally to achieve some benefit. It then defines key terms like exporting, importing, trade surplus and deficit. It goes on to describe several theories of international trade, including mercantilism, absolute advantage, comparative advantage, product life cycles, strategic trade, and diamond theory. The document also discusses sources of comparative advantage, realities of trade such as tariffs and non-tariff barriers, and arguments for and against free trade. It questions whether classical trade theories still apply given new realities of international commerce.