Zittrain works in several intersections of the Internet with law and policy including intellectual property, censorship and filtering for content control, and computer security.

[1] In 2001 he helped found Chilling Effects, a collaborative archive created by Wendy Seltzer to protect lawful online activity from legal threats.

In 2004 with Jennifer K. Harrison, Zittrain published The Torts Game: Defending Mean Joe Greene, a book the authors dedicated to their parents.

[4][5] His sister, Laurie Zittrain Eisenberg, is a scholar of the Arab and Israeli conflict[6] and teaches at Carnegie Mellon University in Pittsburgh.

[8] He holds a bachelor's summa cum laude in cognitive science and artificial intelligence from Yale University, 1991, where he was a member of the Yale Political Union, Manuscript Society and Davenport College, a JD magna cum laude from Harvard Law School, 1995, where he was the winner of the Williston Negotiation Competition, and a Master of Public Administration from Harvard's John F. Kennedy School of Government, 1995.

[18] Although he describes their approach as, in some ways, simple and naïve, Zittrain sees more hope in the open Internet Engineering Task Force model and in the ethical code and assumption of good faith that govern Wikipedia.

In their tests during 2002, when Google had indexed almost 2.5 billion pages, they found sites blocked, from approximately 100 in France and Germany to 2,000 in Saudi Arabia, and 20,000 in the People's Republic of China.

[24] Building on the work completed at the Berkman Center, ONI published special reports, case studies, and bulletins beginning in 2004,[25] and as of 2008, offered research on filtering in 40 countries as well as by regions of the world.

[15][29] Since 2002, researchers have been using the clearinghouse (renamed "Lumen" in 2015) to study the use of cease-and-desist letters, primarily looking at DMCA 512 takedown notices, non-DMCA copyright, and trademark claims.

[30][31] On October 9, 2002, Zittrain and Lawrence Lessig argued a landmark case, known as Eldred v. Ashcroft, before the United States Supreme Court.

The court found that the act did "not exceed Congress' power" and that "CTEA's extension of existing and future copyrights does not violate the First Amendment".

[33] In 2003 Zittrain said he was concerned that Congress will hear the same arguments after the 20-year extension passes, and that the Internet is causing a "cultural reassessment of the meaning of copyright".

[35] When its scans find dangerous code, Google places StopBadware alerts in its search results and rescans later to determine whether a site thereafter had been cleaned.

[43] Directed by Palfrey and Zittrain, StopBadware received high-level guidance from its advisory board: Vint Cerf of Google, Esther Dyson, George He of Lenovo, Greg Papadopoulos (formerly CTO of Sun Microsystems), and Ari Schwartz of the Center for Democracy and Technology.

[46] In February 2019, Zittrain interviewed Facebook CEO Mark Zuckerberg as part of a seminar for students at Harvard on the internet and society.