Many scholars have commented that the state action doctrine forecloses use of the First Amendment to constrain the policies and practices of online service providers. But few have comprehensively studied this issue, and the seminal article exploring “[c]yberspace and the [s]tate [a]ction [d]ebate” is fifteen years old, published before the U.S. Supreme Court reformulated the federal approach to state action. It is important to give the state action doctrine regular scholarly attention, not least because it is increasingly clear that “the private sector has a shared responsibility to help safeguard free expression.” It is critical to understand whether the First Amendment has a role to play in the private sector, as Internet companies continue to develop and enforce their own content rules—as “lawyers at Facebook and Google and Microsoft” exercise “more power over the future of . . . free expression than any king or president or Supreme Court justice.” They are the “sovereigns of cyberspace.” This Article analyzes the state action doctrine as it exists today, examining: (1) how it distinguishes the public and private spheres, and (2) whether it forecloses the First Amendment’s application to nongovernmental Internet companies, specifically third–party platforms like Facebook and Twitter. The Article concludes that the state action doctrine does foreclose such an application. And with that in mind, the author suggests a state action theory suitable for the digital world.