For at least thirty years the Supreme Court has adhered to its third-party doctrine in interpreting the Fourth Amendment, meaning that so far as a disclosing party is concerned, information in the hands of a third party receives no Fourth Amendment protection. The doctrine was controversial when adopted, has been the target of sustained criticism, and is the predominant reason that the Katz revolution has not been the revolution many hoped it would be. Some forty years after Katz the Court's search jurisprudence largely remains tied to property conceptions. As I have demonstrated elsewhere, however, the doctrine is not the universal constitutional rule in the United States. Eleven states reject the doctrine, providing some constitutional search and seizure protection to information in the hands of third parties, and another eleven give some reason to believe they might reject it.

But it is one thing to urge that some third-party information should by protected, and quite another to articulate how and when different information should be accessible to police. To answer this question it makes sense to turn to the most robust source of practical applications we have, namely those states that have diverged from the federal doctrine. Although state courts often employ a gestalt jurisprudence that defies precise delineation, an analysis of many cases reveals a set of relevant factors that would seem to be consistently useful in determining whether law enforcement access should be restricted, and if so in what manner. What such analysis does not reveal is a tidy system of bright-line delineations, seemingly at odds with two thoughtful alternatives to the current federal doctrine proposed by Daniel Solove and Christopher Slobogin.

Part I of this article frames the discussion via recent events. The realization that the National Security Agency has been parsing phone conversations, dialing records, and banking records since the terrorist attacks of September 11, 2001, demonstrates that the third-party doctrine is very much a contemporary concern. The decision last term in Georgia v. Randolph demonstrates that five members of the Supreme Court are willing to depart from the doctrine, at least in the context of the home. Part II then utilizes the existing state (and to a limited extent federal) jurisprudence to determine and explain what factors are relevant in determining whether to constitutionally restrict law enforcement access. This yields an uncertain calculus that also logically challenges the essentially unrestricted ability of law enforcement to probe the recollection of a recalcitrant witness. In Part III I compare my approach to the seemingly more administrable proposals of Professors Solove and Slobogin. I conclude with a tentative defense of the current multi-faceted - and therefore necessarily uncertain - jurisprudence. Although its administrability is imperfect, it more appropriately distinguishes between and among different types and amounts of third-party information.