Judicial review is the doctrine under which legislative and executive actions are subject to review by the judiciary. Specific courts with judicial review power must annul the acts of the state when it finds them incompatible with a higher authority. Judicial review is an example of the separation of powers in a modern governmental system. This principle is interpreted differently in different jurisdictions, so the procedure and scope of judicial review differs from state to state.
Judicial review can be understood in the context of two distinct—but parallel—legal systems, civil law and common law, and also by two distinct theories on democracy and how a government should be set up, legislative supremacy and separation of powers. Common law judges are seen as sources of law, capable of creating new legal rules and rejecting legal rules that are no longer valid. In the civil law tradition, judges are seen as those who apply the law, with no power to create or destroy legal rules.
The separation of powers is another theory about how a democratic society's government should be organized. First introduced by French philosopher Charles de Secondat, Baron de Montesquieu (Figure 1), separation of powers was later institutionalized in the United States by the Supreme Court ruling in Marbury v. Madison. It is based on the idea that no branch of government should be more powerful than any other and that each branch of government should have a check on the powers of the other branches of government, thus creating a balance of power among all branches of government. The key to this idea is checks and balances. In the United States, judicial review is considered a key check on the powers of the other two branches of government by the judiciary.