World currencies, including the US dollar, euro, and Japanese yen, play an important role in the global economy. They are not only a medium of exchange, but also a symbol of trust and stability. The US dollar, as the main reserve currency, represents approximately 60% of global foreign exchange reserves, influencing international trade and investment. This currency facilitates efficient international transactions. When multinational companies operate in different countries, they often use stable currencies such as the dollar. This reduces the risk of exchange rate changes and provides certainty in financial planning. In addition, the existence of an international payment system, such as SWIFT, guarantees security and speed of transactions. The role of currency is also revealed in commodity trading. Most commodities, such as oil and precious metals, are traded in US dollars. This creates a constant demand for dollars, maintaining its stability in the long term. As demand increases, commodity producing countries can accumulate foreign exchange reserves, contributing to the growth of their domestic economies. World currencies also function as monetary policy tools. Central banks use interest rates and market intervention to influence the exchange rates of their currencies. For example, when the US Federal Reserve raises interest rates, the value of the dollar tends to strengthen. This has an impact on the global economy because it can affect capital flows and foreign direct investment. Exchange rate fluctuations can have far-reaching impacts. Countries with strong currencies may experience reduced competitiveness in export markets, while a weak currency may increase exports by making goods more affordable for international buyers. This creates complex dynamics in global trade and influences the economic policies of each country. Economic crises, such as recessions, also affect preferences for world currencies. Investments in times of crisis tend to shift to safer currencies, such as the US dollar or Swiss franc, creating asset flight. This increases demand for the currency, causing significant exchange rate fluctuations. Technological developments are also changing the world currency landscape. The emergence of cryptocurrencies offers new alternatives in the financial system. Although still in its early stages, the adoption of digital currencies could shift international transaction patterns and reduce dependence on fiat currencies. The relationship between world currencies and the global economy is very complex. Any change in this currency can produce far-reaching impacts, affecting from individual micro to global macro scales. In studying economics, it is important to understand these relationships so that we can be better prepared to deal with changing market dynamics.