Grouping express and implied powers together, the more important powers of Congress may be summarized as follows:
Revenue and expenditures. Congress has the power to lay and collect taxes, duties, imports, and excises, and to appropriate money in order "to pay the debts and provide for the common defense and general welfare of the United States." But indirect taxes must be uniform throughout the United States, and all direct taxes, except income taxes, must be apportioned among the states according to population. A further limitation is that Congress may not tax exports from any state, nor levy upon the "necessary instrumentalities" of any state government.
National defense. Here the powers of Congress are practically unlimited, except by the constitutional provisions that the President shall be commander-in-chief, and that military appropriations shall not be made for more than two years. Congress can raise and support armies, create and maintain a navy, and provide for the organization and use of the state militia. Congress may also declare war, and make rules concerning captures on land and sea.
Foreign relations. Congress as a body has little direct control over foreign relations, though the Senate shares the treaty-making power with the President. But Congress has the power to create diplomatic and consular posts, as well as "to define and punish piracies and felonies committed on the high seas, and offences against the law of nations." Congress also exercises control over immigration and naturalization.
Economic interests. Congress may regulate commerce with foreign countries, among the several states, and with the Indian tribes. The exclusive power to coin money, and otherwise control the monetary system, is vested in Congress. Congress may make uniform laws on bankruptcy throughout the United States, and fix the standards of weights and measures. The establishment of post offices and post roads, and the protection of authors and inventors through legislation on patents and copyrights, are also functions of Congress.
Territories. Congress has the power to dispose of, and make all needful rules and regulations respecting, the territory or other property belonging to the United States. Congress likewise exercises exclusive control over the District of Columbia, and over all places purchased by the Federal government for the erection of forts, arsenals, and similar buildings. Congress also has the right to determine the admission to the Union of new states, and "to dispose of and make all needful rules and regulations respecting the territory or other property belonging to the United States."
Crime. In criminal matters the power of Congress is slight. For example, it cannot say what constitutes treason, since that crime is defined by the Constitution. However, Congress may provide for the punishment of counterfeiters and persons committing crimes on the high seas or offences against international law. It may also define certain crimes against Federal law, and prescribe penalties therefor.
Control over the judiciary. The judiciary is an independent branch of government, but Congress may determine the number of Supreme Court judges, fix their salaries within certain limits, and define their appellate jurisdiction. Congress may also determine the jurisdiction, and define the procedure, of the inferior Federal courts.
Implied powers. Last among the powers of Congress is the authority granted to it by the Constitution to make all laws which shall be deemed necessary and proper for carrying into execution the powers expressly granted to Congress by the Constitution. It is under the authority of this clause, that the implied powers of Congress have been so greatly expanded.