He is a New York writer, author of "Now They Tell Us" (2004), a collection of articles published in the New York Review of Books about the press coverage of the war in Iraq. He is also author of "The Fix" (1998), a critical study of the U.S. war on drugs. It was named co-winner of the Washington Monthly's Political Book Award for 1998. In addition to The New York Review of Books, he has written for The New York Times Magazine, The New Yorker, The Atlantic Monthly, The Washington Post, The Los Angeles Times, The Nation, The American Prospect, The New Republic, The Washington Monthly, and Rolling Stone.

He is a former executive editor of the Columbia Journalism Review and remains a contributing editor at that publication.

He has served as an adjunct professor at the Columbia School of Journalism and at the Columbia School for International and Public Affairs. He is co-founder of the Committee To Protect Journalists and currently sits on its board of directors. He is a member of PEN America and of the New York Institute for the Humanities.

The holder of a bachelor's degree from Harvard College and a master's degree from the London School of Economics & Political Science, Massing in 1989 was awarded an Alicia Patterson journalism fellowship, and in 1992 he was named a MacArthur Fellow.

He is currently working on a book about the rivalry between Erasmus and Martin Luther and its impact on European thought and society.