What was the most important aspect of the supreme court case in marbury v. s. madison

Marbury v. Madison, legal case in which, on February 24, 1803, the U.S. Supreme Court first declared an act of Congress unconstitutional, thus establishing the doctrine of judicial review. The court's opinion, written by Chief Justice John Marshall, is considered one of the foundations of U.S. constitutional law.

Abecause it’s just i.s. i learned this