Reserved powers

Reserved powers, residual powers, or residuary powers are the powers that are neither prohibited to be exercised by an organ of government, nor given by law to any other organ of government. Such powers, as well as a general power of competence, nevertheless may exist because it is impractical to detail in legislation every act allowed to be carried out by the state.

Common law countries
The United Kingdom and countries whose legal system is based on common law, such as Canada, India, Israel, and Ireland, have similar legal frameworks of reserved powers.

Australia
In Australia, despite the centralized nature of the constitution, the High Court adopted the "reserved powers doctrine" which was used until 1920 to preserve as much autonomy for the states as can be interpreted from the constitution. This practice changed with the Engineers' Case which led reserved powers to be given to the Commonwealth.

Canada
In Canada the reserved powers lie with the federal government.

United States
In the United States, the Tenth Amendment of the Constitution states that the powers not granted to the federal government are reserved to the states, unless prohibited to the states. This amendment does not refer to powers “explicitly” or “expressly” granted to the federal government, and therefore the federal government possesses many implied powers that are not reserved to the states.

After World War II, the Supreme Court often ruled against parties challenging the powers of Congress per the Tenth Amendment, with exceptions during the Rehnquist Court. The Supreme Court continues to occasionally decide cases striking down federal laws that exceed both the explicit and implied powers of Congress, as in Murphy v. National Collegiate Athletic Association (2018).

In the United States, many powers that are not reserved to the states are exclusive federal powers, and thus states are forbidden to exercise them. Alternatively, powers that are not reserved to the states may be concurrent powers that both the states and federal government can exercise at the same time (such as the power to enact taxes to raise revenue).