Social network websites such as Facebook and Twitter have assumed a place of great importance in contemporary social life and politics, transforming how individuals interact with each other and how social and political movements organize and communicate with the broader public. While thus far social network websites have served as open and free forums for speech and debate, they face a number of internal and external pressures to engage in censorship. This Article argues that federal courts can and should extend First Amendment protections to communications on social network websites. Communications on social network websites are especially deserving of protection under the First Amendment because they invoke the freedoms of speech, press, and association, and because social network websites strongly resemble the spaces that the Supreme Court has protected under the public forum doctrine. However, because social network websites are privately owned, actions by social network websites to censor content would ordinarily fall outside the ambit of the Constitution’s protections. Nevertheless, courts can and should treat social network websites as state actors under the public function exception to the state action doctrine and, when appropriate, the entwinement exception to the state action doctrine.