Fundamentals

Constitutional Review: What It Is, Its Types, and Why It Limits Power

By Daniel Sardá · Published on September 12, 2026

7 min read1,396 words

Constitutional review measures laws and public decisions against the Constitution. Its models, effects, and limits matter as much as its existence.

A law enacted by a majority may conflict with a rule that the political community itself has placed above ordinary legislation. An administrative authority may likewise exceed the powers the Constitution grants it. Constitutional review encompasses the avenues through which such conflicts are examined and the consequences each legal system provides.

It is not, by itself, a promise of good government or the universal name for a specialized court. It is an institutional technique: it compares a rule, act, or public decision against the Constitution as the higher standard. Its value depends on who may trigger it, who decides, what effect the decision has, and whether those rules operate independently.

Why constitutional supremacy needs a mechanism

To say that the Constitution is supreme has a practical consequence: a lower-ranking rule should not displace it merely because it was enacted later, received more votes in a legislative chamber, or is convenient for the authorities of the day. But a written hierarchy does not, by itself, resolve conflicts. An institution or procedure must be able to ask the relevant question: is this measure compatible with the Constitution?

Judicial review in the United States is historically associated with the idea that the Constitution prevails over incompatible legislation, following Marbury v. Madison, as the U.S. Supreme Court explains. The principle, however, does not require every country to use the same institutions or give its judgments the same scope.

Key idea: Constitutional supremacy does not mean that every public decision is reviewed; it means that defined avenues exist to review those the Constitution subjects to scrutiny.

The standard is not always reducible to an isolated phrase in the constitutional text. It may require reading powers, rights, procedures, and principles together with the interpretive rules accepted by the system itself. This calls for caution: political disagreement with a law is not, by itself, enough to make it a constitutional question.

This institutional architecture is part of liberal constitutionalism: power is exercised under prior, general rules, not merely according to the passing will of those who govern. Even so, the review mechanism should not be confused with constitutional theory as a whole or with the constitutional guarantees available to protect rights.

Who reviews: concentrated, diffuse, and mixed models

The first distinction answers a simple question: which body has authority to decide constitutionality? The Venice Commission describes comparative models but notes that, in practice, countries employ a range of combinations. These categories are therefore guides; they do not replace studying each country’s rules.

Concentrated review

In a concentrated model, the decision is assigned primarily to a specialized body—often a constitutional court or tribunal—or to a supreme court with that power. The advantage of concentration is that it may offer an institutionally uniform answer about the meaning of the Constitution. Access, however, may be reserved for particular public bodies, parliamentary minorities, or individuals who meet specific requirements.

Spain provides a recognizable example. Its Constitution gives the Constitutional Court, among other matters, jurisdiction over challenges to the constitutionality of laws and measures with the force of law, constitutional questions, and amparo in the cases provided by law (Articles 161–164, BOE). This allocation of powers describes the Spanish case; it does not make amparo a universal category or, by itself, define other systems.

Diffuse review

In a diffuse model, a constitutional issue may arise before ordinary judges as they decide a particular dispute. The judge does not necessarily need to wait for a separate body to identify the relevant incompatibility in the case. The U.S. tradition of judicial review is the best-known comparative reference.

This does not mean that every judge, in every country, may invalidate a law with general effect. In several arrangements, the consequence may be not to apply the rule to the case at hand. Jurisdiction, further review, and the scope of the judgment are separate questions.

Mixed systems

Many legal systems combine elements: ordinary judges may raise a constitutional question while a specialized body decides it with specified effects; direct actions may coexist with questions arising from litigation. Calling them mixed helps avoid forcing comparative reality into two closed boxes.

Key idea: Concentrated, diffuse, and mixed primarily describe the allocation of authority; they do not yet tell us when a rule is reviewed or what will follow from the judgment.

When and how a rule is reviewed

Other distinctions organize the procedure rather than the institutional model. Keeping them separate prevents one form of review from being confused with an institution.

• Prior and subsequent review. Prior review takes place before a rule fully takes effect; subsequent review occurs once it is in force or has produced consequences. Each system determines which measures it admits at either stage.
• Abstract and concrete review. Abstract review addresses a rule without necessarily requiring the resolution of an individual’s particular dispute. Concrete review arises within a controversy, and the constitutional answer affects how that case is decided.
• Procedural and substantive review. Procedural review asks, for instance, whether constitutional authority or the required enactment process was respected. Substantive review assesses the measure’s content against constitutional rights, limits, or commands.

A single controversy may involve more than one dimension. A law may be challenged because it was enacted without the required procedure and because it restricts a right incompatibly. These classifications bring order to the discussion; they do not replace reasoning about the applicable constitutional text.

What a finding of unconstitutionality can produce

The effect of a decision is perhaps the most important distinction for readers. The word “unconstitutional” does not automatically produce the same result in every country.

In some procedures, the decision may deprive a rule of force or declare it invalid with general effect. In others, it may prevent the rule from being applied to the parties in a particular dispute. It may also favor a constitutionally conforming interpretation: among several possible readings, the one that conflicts with the Constitution is rejected and a compatible interpretation is preserved, where domestic law permits it.

A useful caution: General invalidity and non-application in a single case are not synonyms. Knowing who decides and under which procedure is essential before stating the scope of a judgment.

This difference explains why institutions from one country should not be mechanically carried over to another. It also prevents constitutional review from being identified with constitutional *amparo*: amparo is a remedy with varied national configurations, whereas review may directly concern rules, acts, or decisions, depending on the applicable design.

Nor should it be confused with conventionality control. Both involve legal comparison, but they do not use the same standard. According to the Inter-American Court of Human Rights, the latter is connected, within the relevant powers, with the American Convention, its interpretation, and other pertinent international obligations; constitutional review takes the state’s Constitution as its primary reference.

A limit on power that also needs limits

From the standpoint of limited government, constitutional review can prevent a temporary majority, a bureaucracy, or even a lower-court ruling from turning a contingent preference into a rule superior to the Constitution. It is an institutional safeguard against arbitrariness, not a license for any judge freely to replace decisions made by representative bodies.

Here a genuine tension appears. Judicial review may set aside decisions made by elected authorities, and for that reason it requires defined jurisdiction, accessible but clear procedures, publicly reasoned decisions, and independence from political pressure. Without those elements, invoking the Constitution can become a selective instrument of power rather than a common rule.

A constitutional government does not consist merely in having judges review laws. It requires legislators, executives, and courts to be subject to known rules, and judgments to be followed for legal reasons rather than affinity with whoever prevails in the dispute. Constitutional review best serves its function when it is a defined power within that system of reciprocal limits.

Understanding it this way changes the opening question. It is not enough to ask whether a constitutional court exists or whether a law has been challenged. What matters is knowing what is reviewed, against which standard, who has the final word in that procedure, and what effect follows. Those concrete rules determine whether the Constitution is an effective limit on power rather than a solemn declaration.