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Over many years, the United States Supreme Court has developed an extensive body of precedent interpreting and enforcing the provisions of the Fourth Amendment to the United States Constitution, which prohibits unreasonable searches and seizures by law enforcement agents conducting criminal investigations. Commonly called the "warrant requirement," one key component of this case law operates to deem some police investigatory techniques to be unconstitutional unless they are conducted pursuant to a search warrant issued in advance by a judge. The terms of the doctrine and its exceptions also authorize other investigatory actions as constitutionally permissible without a search warrant. The doctrinal framework created by the warrant requirement serves as a core foundational principle of the Court's constitutional criminal procedure for police investigations. The conventional wisdom about the warrant requirement suggests that over the last half-century, the Court has moved from rigorously interpreting and enforcing the doctrine to reducing its importance and recognizing more exceptions for permissible warrantless searches. While this perspective has some descriptive accuracy in the aggregate, the past decade of the Roberts Court has produced a series of Fourth Amendment decisions, ranging across a variety of subsidiary doctrinal areas, where the warrant requirement has made a comeback-cases in which a criminal defendant has prevailed because the police lacked a search warrant when acquiring crucial evidence during the investigation. A common thread among these decisions is the Roberts Court's confrontation of the Fourth Amendment implications of electronic surveillance, internet connectivity, data analytics, and other rapidly advancing technologies in the digital age. This resurgence of the warrant requirement cannot be readily dismissed as happenstance or coincidence, and consequently its development and its future ramifications are worthy of careful consideration.