Final answer:
The landmark case of Marbury v. Madison is significant due to the court's ruling on the establishment of judicial review.
Step-by-step explanation:
Judicial review is the power of a court to examine and potentially invalidate governmental actions, such as laws or executive decisions, that are deemed unconstitutional or inconsistent with established laws. The landmark case of Marbury v. Madison is considered significant mostly because of the court's ruling on the establishment of judicial review.
Chief Justice John Marshall's decision in 1803 established the principle that the Supreme Court has the power to review and possibly nullify the actions of Congress and the President if they are found to be unconstitutional. Therefore, the ruling in Marbury v. Madison affirmed the Court's role in interpreting the Constitution and ensuring the separation of powers among the branches of government.