As Julian Sanchez explains, the third-party doctrine holds that the information that individuals disclose to businesses — credit card transactions, phone records, etc. — doesn’t carry with it a “reasonable expectation of privacy” under the Fourth Amendment, as one has “assumed the risk” that this information might at some point be disclosed. Technological innovation has meant that this third-party doctrine has vastly expanded the government’s surveillance powers:

When you buy a book, join a political e-mail list or read a website, a third-party record is created. Even the contents of your private messages or files stored in the “cloud” aren’t really yours, according to this doctrine. Federal law allows them to be obtained without a search warrant in many circumstances. Those old phone logs, meanwhile, have become far more revealing with the advent of cellular technology, which can track your geographical movements in increasingly precise detail. The result is that a vast array of private information that would previously have required a physical search — and therefore a search warrant — to obtain is now available under a far lower standard. And much of that data concerns domains of speech and intimate association traditionally held to be protected by the First Amendment as well.

Julian notes that at least one prominent jurist, Justice Sonia Sotomayor, has suggested that “it may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties,” an extremely encouraging development, and further indication that Justice Sotomayor has proven a valuable addition to the Supreme Court. Eli Dourado has more on the implications of the third-party doctrine in the age of cloud computing.