Books are banned in the society depicted in Fahrenheit 451. When they're found, they're burned, along with the homes of the books' owners. But it's important to remember that in the world of this novel, the suppression of books began as self-censorship. As Beatty explains to Montag, people didn't stop reading books because a tyrannical government forced them to stop. They stopped reading books gradually over time as the culture around them grew faster, shallower, intellectually blander, and centered around minor thrills and instant gratification. In such a culture, books became shorter, magazine and newspaper articles became simpler, cartoon pictures and television became more prevalent, and entertainment replaced reflection and debate.
Another factor that contributes to the growth of censorship in Fahrenheit 451 are minorities and what we might call "special interest groups." In order not to offend every imaginable group and sub-group—whether organized around ethnicity, religion, profession, geography, or affinity—every trace of controversy slowly vanished from public discourse, and magazines became "a nice blend of vanilla tapioca." In time, the word "intellectual" became a swear word, and books came to be seen as a dangerous means for one person to lord his or her knowledge and learning over someone else. Books, and the critical thinking they encouraged, became seen as a direct threat to equality. By making widespread censorship a phenomenon that emerges from the culture itself—and not one that is simply imposed from above by the government—Bradbury is expressing a concern that the power of mass media can ultimately suppress free speech as thoroughly as any totalitarian regime.