Search engines map the incalculably vast territories of the Internet and provide search results to queries, allowing users to easily find what they are looking for.
Because search engines have now become virtually indispensable, they are increasingly magnets for censorship. This damages search neutrality, which ensures that users get the results they were looking for (as opposed to what governments or private actors want them to see), and makes it harder for online speakers to disseminate their views.
Authoritarian governments often block search engines or force them to blacklist certain queries to limit access to what the governments perceive as threatening or subversive materials. Industry groups that lobby for increased copyright holder control, like the MPAA and the RIAA, have also realized the power of search censorship, for example, challenging torrent search indices such as isoHunt. In addition to these large players, individuals may claim that search engine results are defamatory or otherwise illegal and seek to have them taken down.
Depending on the jurisdiction, such efforts may or may not enjoy the support of law. In the United States, for example, the First Amendment and Section 230 of the Communications Decency Act make efforts to remove non-copyrighted material difficult, although notices of copyright infringement (valid or not) are facilitated by easy to use (and easy to abuse) procedures provided by the DMCA. Processes initiated in other countries with weaker legal protections may lead to easier removal of speech.
The Chinese government forces search engines like the immensely popular Chinese search engine Baidu.com to edit certain search results. Without an easy way to find it, the blocked information may as well not exist.