What is the most important power of Congress?

The most important power of Congress is the authority to make laws. A bill, also known as a proposed law, only becomes an official law after the House of Representatives and Senate have both approved it.

All of the powers held by the U.S. Congress are listed in Article 1, Section 8 of the Constitution of the United States of America. In addition to the power to make and approve laws, Congress also holds the power to declare war, regulate commerce and coin money, establish the rules of naturalization and immigration, raise an Army or Navy and to establish federal courts.