Shortly after the September 11, 2001, attacks, Eli Pariser created a website calling for a multilateral approach to fighting terrorism. In the following weeks, over half a million people from 192 countries signed on, and Pariser rather unexpectedly became an online organizer. The website merged with MoveOn.org in November 2001, and Pariser -- then 20 years old -- joined the group to direct its foreign policy campaigns. He led what the New York Times Magazine called the "mainstream arm of the peace movement" -- tripling MoveOn's member base and demonstrating how large numbers of small donations could be mobilized through online engagement.

In 2004, Pariser became executive director of MoveOn. Under his leadership, MoveOn.org Political Action has grown to 5 million members and raised over $120 million from millions of small donors to support advocacy campaigns and political candidates. Pariser focused MoveOn on online-to-offline organizing, developing phone-banking tools and precinct programs in 2004 and 2006 that laid the groundwork for Barack Obama's extraordinary web-powered campaign. In 2008, Pariser transitioned the Executive Director role at MoveOn to Justin Ruben and became President of MoveOn’s board; he's now a senior fellow at the Roosevelt Institute.

His book The Filter Bubble is set for release May 12, 2011. In it, he asks how modern search tools -- the filter by which many of see the wider world -- are getting better and better and screening the wider world from us, by returning only the search results it "thinks" we want to see.