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 Oregon, 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 U.S. Constitution takes precedence over any state laws in areas where the federal government has been granted authority. It outlines the structure and powers of the federal government, including the legislative, executive, and judicial branches, and their checks and balances. Additionally, it delineates the relationships between the states, between states and the federal government, and between individuals and both levels of government. The Constitution can be amended according to the process outlined in Article V, with the first ten amendments known as the Bill of Rights. While Oregon has its own state constitution, which governs the state's laws and government, references to 'constitutional law' without further specification typically pertain to the U.S. Constitution. Oregon's state constitution must comply with the U.S. Constitution, and any conflicts are resolved in favor of the federal Constitution due to the Supremacy Clause.