Once passed by the legislature and signed into law by the president, the people of the United States can challenge any law in the courts under the authority of the judicial branch. Laws deemed unconstitutional by the judiciary are considered void. In this way, justices of the courts become the final arbiters of the fairness and legality of a law's provisions.
In 1803, the case of Marbury v. Madison enshrined the principle of judicial review in American law. Judicial review grants the courts the right to establish the consistency of any statute with existing laws and constitutional requirements. Authoring the unanimous opinion, Supreme Court Chief Justice John Marshall asserted the duty of the court to strike down a law deemed unconstitutional — in this case, the provision that allowed Marbury to bring his suit before the court in the first place.
In the centuries since Marbury v. Madison, the Supreme Court has heard tens of thousands of cases and has made controversial decisions with ramifications that affect American culture for generations. Hundreds of thousands more cases have been decided by lower levels of the judiciary. However, the path to change laws through the judiciary is not an immediate one. While laws are often debated, voted on in the legislature over matters of days or weeks, many appeals to the Supreme and appellate courts take months or years of preparation, and many more are never heard at all.