Constitutional theory is an area of constitutional law that focuses on the underpinnings of constitutional government. It overlaps with legal theory, constitutionalism, philosophy of law and democratic theory. It is not limited by country or jurisdiction.
Constitutional theory in the United States is an academic discipline that focuses on the meaning of the United States Constitution. Its concerns include (but are not limited to) the historical, linguistic, sociological, ethical, and political.
Much of constitutional theory is concerned with theories of judicial review. This is in part because Marbury v. Madison, which established this judicial power in the early 19th century, has given the judiciary near-final authority on constitutional meaning.
Aside from judicial review, constitutional theory in general seeks to ask and answer the following questions:
Although constitutional theory as a discipline has its precursors in The Federalist and Justice Story's Commentaries on the Constitution, modern constitutional theory began with the publication of Alexander Bickel's The Least Dangerous Branch. (The title is an allusion to The Federalist No. 78, in which Alexander Hamilton wrote that the judiciary "will always be the least dangerous to the political rights of the Constitution", because it has neither the sword (like the Executive) nor the purse (like the Legislature). The book's primary (but not sole) contribution was to introduce the idea of the "countermajoritarian difficulty." The idea expressed by the term countermajoritarian difficulty is that there is a tension between democratic government (as he defines it democratic government is majoritarian government) and judicial power. If the judiciary—an unelected branch of government—can overturn popular legislation, then either there is a fundamental contradiction within the democratic system, or there is a tension that must be resolved by curbing judicial power. (One of Bickel's solutions is for the Court to exercise "the passive virtues": that is, to decline to decide more than it has to decide.)