Prime purpose of this lecture is to Presentation on International Trade Theory. Here explain all these theories in international business perspective. International trade is exchange of raw materials and manufactured goods and services across national borders. Here briefly discuss on various International Trade Theory, like: Classical trade theories, New trade theories, Mercantilism theory and Free Trade theories. This lecture also explain theory of Relative Factor Endowments and international Product Life-Cycle. Finally analysis Porter’s Diamond with proper examples and explanation.