Abstract: In addition to “persons, houses, [and] papers,” the Constitution protects individuals against unreasonable searches and seizures of “effects.” However, “effects” have received considerably less attention than the rest of the categories in the Fourth Amendment. Recent Supreme Court opinions on Fourth Amendment searches reintroduced the word “effects,” and yet they did so without a definition of the word, an understanding of its history, or a clear doctrinal theory. In the absence of a coherent approach to “effects,” many lower courts apply the standard Fourth Amendment test: they ask whether the government has violated the claimant’s “reasonable expectation of privacy.” However, many lower courts protect or decline to protect personal property by examining the individual’s expectation of privacy in the property’s physical location. These courts hold that individuals have no expectations of privacy in personal property that is unattended in public space. This Article argues that personal property in public space should receive greater constitutional protection than is provided by these cases, because of the privacy and security interests inherent in ownership and possession. The history surrounding the Fourth Amendment provides evidence that the protection against unreasonable searches and seizures was connected to the law prohibiting interferences with another’s possession of personal property, including dispossession, damage, or unwanted handling. To restore this connection, this Article uses guidance from personal-property law to propose a framework for identifying Fourth Amendment interests in effects based on their qualities and environment. This intervention would grant effects the constitutional protection they deserve.