In the last 25 years, the U.S. Supreme Court’s treatment of the Fourth Amendment issues underwent a shift in philosophy that resulted in a conservative body of search and seizure law that was very different from the more liberal search and seizure law that was developed by the Warren Court in the 1960's. This article examined the most important Fourth Amendment cases decided by the Warren Court and by the post-Warrant Court (1975–2000). One of the most important Warren Court Fourth Amendment decisions was Mapp v. Ohio (1961). In this case, the Court held that States must apply the exclusionary rule to evidence obtained unconstitutionally. Mapp became a focal point for the States’ resentment of the intrusion of the Federal courts into criminal matters, an area that States believed had been left to their control. Additional Warren Court decisions discussed included: Aguilar v. Texas (1964); Katz v. U.S. (1967); Chimel v. California (1969); Camara v. Municipal Court (1967); Terry v. Ohio (1968); and Warden v. Hayden (1967). Since 1974, the Supreme Court had decided more than 140 cases involving issues arising under the Fourth Amendment. The decisions discussed steered the law significantly in a direction different from that of the Warren Court, or had held in favor of the criminal defendant in a significant way that stood out from the general trend reflected in post-Warren Court decisions. It was concluded that the post-Warren Court had been very pro-police in its approach to Fourth Amendment issues, had developed a body of conservative case law in this area while overturning only one of the controversial Warren Court decisions, had often made only minor changes to Fourth Amendment jurisprudence that had nevertheless conveyed a message that constitutional restraints on the police had been relaxed, and had been consistent in its conservative approach to Fourth Amendment issues.