In 1987, the Federal Bureau of Investigation approached Columbia University librarian Paula Kaufman with a request: Keep an eye out for commies.

She refused to cooperate with the bureau's "library awareness" program and her defiance helped spark a nationwide backlash against government snooping into Americans' reading habits. Even knowing the government might be watching, people realized, could change what you choose to read—and in turn alter what you think. As a result of similar incidents that occurred over the years, 48 states now have laws on the books protecting library records, and the other two have legal directives in place that uphold similar standards. (The protections vary from state to state.)