Constitutional law is generally the interpretation and application of the United States Constitution, which is the supreme law of the land, and supersedes (preempts) all state laws on matters in which the U.S. Constitution grants the federal government authority. The Constitution is the foundation of the U.S. legal system, and defines (enumerates) the powers of the three branches of government (legislative, executive, and judicial) and each branch’s oversight of the others. The Constitution also defines the relationships between states; between states and the federal government; and between individuals and the state and federal governments.

The Constitution may be amended as provided by Article V, and the first ten amendments were ratified by the states in 1791 and are known as the Bill of Rights.

Constitutional law may also be a reference to state constitutions, but when not specifically indicated, it is considered a reference to the U.S. Constitution.

In Maryland, as in all states, constitutional law refers to the interpretation and application of the U.S. Constitution, which is the paramount law of the country. The Constitution outlines the powers and responsibilities of the federal government's three branches—legislative, executive, and judicial—and establishes checks and balances among them. It also delineates the powers of the federal government and the states, ensuring that federal law preempts state law in areas where the federal government has been granted authority. Maryland's state laws and constitution must comply with the U.S. Constitution. The Bill of Rights, consisting of the first ten amendments to the Constitution, protects individual liberties and rights from government infringement. While Maryland has its own state constitution, which governs the structure and function of the state government and provides additional protections to its residents, it cannot conflict with the U.S. Constitution. Amendments to the U.S. Constitution are possible through the process outlined in Article V, which requires a high threshold of agreement among the states and/or Congress, reflecting the document's foundational status in the American legal system.