On September 12, 2001, Eli Pariser sent an e-mail to thirty friends asking them to contact their senators and representatives with a message that revenge and more violence weren’t the answer to the terrorist attacks. He provided the recipients with an online form letter that enabled them to act quickly. He was twenty, a recent college graduate living in an apartment in Boston. It felt like something he could do.

The e-mail set off a chain of events that would lead Pariser to devote himself to a new kind of political organizing, one that reaches people through their e-mail in-boxes. Through its antiwar efforts, MoveOn.org, the group for which Pariser now works, has grown to 1.6 million members in the United States.