Communication Ethics book part for United States Legal Basis. (This is an automatically generated summary to avoid having huge posts on this page. Click through to read this post.)

In the United States, the right to privacy derives from the Fourth Amendment to the United States Constitution, which is part of the Bill of Rights:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

You can see the word "privacy" never directly appears in the Amendment but based on the definition above ("freedom from unauthorized intrusion"), it's clear how this relates to a person's right to privacy from the government. The doctrine of privacy has subsequently been heavily interpreted by the Supreme Court, in ways that can and have been themselves the subject of lengthy books.