Foreign direct investment (FDI) involves investing directly in a foreign business by acquiring ownership or control, while portfolio investment refers to the purchase of financial assets, such as stocks and bonds, in foreign markets without the intent of gaining control. FDI often leads to a significant presence and influence in the foreign market, whereas portfolio investment is typically more passive and focused on financial returns. Both types of investment play crucial roles in international economics, affecting capital flows, exchange rates, and economic growth in both home and host countries.